Leafflower–leafflower moth mutualism in the Neotropics: Successful transoceanic dispersal from the Old World to the New World by actively-pollinating leafflower moths

In the Old World tropics, several hundred species of leafflowers (Phyllanthus sensu lato; Phyllanthaceae) are engaged in obligate mutualisms with species-specific leafflower moths (Epicephala; Gracillariidae) whose adults actively pollinate flowers and larvae consume the resulting seeds. Considerable diversity of Phyllanthus also exists in the New World, but whether any New World Phyllanthus is pollinated by Epicephala is unknown. We studied the pollination biology of four woody Phyllanthus species occurring in Peru over a period of four years, and found that each species is associated with a species-specific, seed-eating Epicephala moth, here described as new species. Another Epicephala species found associated with herbaceous Phyllanthus is also described. This is the first description of Epicephala from the New World. Field-collected female moths of the four Epicephala species associated with woody Phyllanthus all carried pollen on the proboscises, and active pollination behavior was observed in at least two species. Thus, Epicephala moths also pollinate New World Phyllanthus. However, not all of these Epicephala species may be mutualistic with their hosts, because we occasionally observed females laying eggs in developing fruits without pollinating. Also, the flowers of some Phyllanthus species were visited by pollen-bearing thrips or gall midges, which potentially acted as co-pollinators or primary pollinators. Phylogenetic analysis showed that the New World Epicephala associated with woody Phyllanthus are nested within lineages of Old World active pollinators. Thus, actively-pollinating Epicephala moths, which originated in the Old World, successfully colonized the New World probably across the Pacific and established mutualisms with resident Phyllanthus species, although whether any of the relationships are obligate requires further study. There is likely a major radiation of Epicephala still to be found in the New World.


Introduction
Obligate pollination mutualism between plants and actively pollinating, seed parasitic pollinators represent some of the most sophisticated examples of plant-pollinator coevolution [1]. Examples include the fig-fig wasp [2,3], yucca-yucca moth [4], and leafflower-leafflower moth mutualisms [5,6], wherein the plants sacrifice a subset of the seeds as nourishment of pollinator larvae in return for pollination services. The pollinating insects have evolved to actively pollinate host flowers to ensure food (developing seeds) for their larvae, and have morphological features that enhance active pollination, such as the coxal comb and pollen pockets in fig wasps [7], maxillary tentacles in yucca moths [8], and hairy proboscis in leafflower moths [9]. Usually a subset of the seeds is left uneaten by the pollinator larvae, providing net benefit of the mutualism for the plants. Plant specializations to these pollinators have led to highly restrictive floral structures and/or loss of nectar reward, making their flowers hardly attractive to ordinary flower visitors.
Leafflowers are the plants in the genera Glochidion, Breynia, and Phyllanthus in the tribe Phyllantheae (Phyllanthaceae), comprising about 1,200 species distributed throughout the Old World and New World tropics [10,11]. The mutualism with leafflower moths, or moths in the genus Epicephala (Gracilariidae), was initially discovered in three species of Glochidion in Japan [5], but later studies showed that as many as 500 leafflower species, occurring throughout tropical Asia, Africa, Australia, and the Pacific, are mutualistic with species-specific, actively pollinating Epicephala moths [12]. These plants bear small (up to 3-4 mm), greenish, unisexual flowers that are visited nocturnally by the females of Epicephala moths. The moth uses the hairy proboscis to actively collect pollen on male flower and deposit pollen on the stigma, after which it lays an egg in the flower that it has just pollinated. In most leafflower species, the number of seeds per fruit is 6 (but can be up to 20 in some Glochidion) [11]. The proportion of the seeds in each fruit consumed by single Epicephala larva is variable among species, but a subset of the seeds usually remains intact after moth consumption [13]. Phylogenetic analysis of the plants and the moths indicated that, whereas the active pollination behavior originated only once in Epicephala, specialization to Epicephala pollination occurred independently in at least five distinct leafflower lineages (Fig 1) [12].
While knowledge on the diversity and evolution of the leafflower-moth association is accumulating in the Old World tropics, virtually nothing is known about the pollination biology of leafflowers in the New World, despite the fact that there are ca. 250 Phyllanthus species throughout the New World. Cuba and Venezuala harbor particularly high diversity with 50 and 58 species, respectively [10]. Molecular phylogenetic analysis suggested that New World Phyllanthus group to into three clades of entirely New World species (Fig 1) [14]. These clades occupy derived positions on the phylogeny (Fig 1), indicating that Phyllanthus plants colonized the New World from the Old World multiple times. Based on divergence time estimation using fossil calibrations [12], New World colonization by Phyllanthus occurred no earlier than the Oligocene (33.9-23.0 Ma). Although the transboreal tropical forest spanning the northern continental area during warm periods of the late Paleocene and early Eocene (ca. 50-52 Ma) [15] would presumably have allowed overland dispersal by these tropical plants, Phyllanthus colonization of the New World is too young to be explained by such a scenario and thus is likely the result of transoceanic dispersal.
Due to dearth of fossil Gracillariidae, the divergence times of Epicephala is much less reliable. However, available estimation based on COI molecular clock suggests that the genus originated around ca. 25 Ma [12]. Thus, the Neotropics was well separated from the Old World tropics by ocean mass by the time actively pollinating Epicephala evolved. Although intercontinental dispersal by tropical insects such as Epicephala seems unlikely, Epicephala has The tree is based on the most recent molecular phylogenetic analyses of the tribe [12,14]. Species richness of each terminal clade is provided as the area of the clade triangle. The five clades repeatedly colonized remote oceanic islands of the Pacific [16], suggesting that intercontinental, transoceanic dispersal may also be feasible. Because presently there are no Epicephala species described from the New World, we set out to determine whether Epicephala occurs in the New World, and if so, whether they are mutualistic with the host Phyllanthus, with an aim to understand the global distribution and diversity of the leafflower-leafflower moth mutualism.

Study sites and materials
The study was conducted in Peru during four field expeditions conducted each year during 2013-2016. The first study site, La Florida (6˚52'05"S, 79˚07'43"W), is located between 900-1,200 m a.s.l. on the western slope of the Andes Mountains and harbors a seasonally dry tropical forest. Three Phyllanthus species, P. salviifolius, P. graveolens, and P. huallagensis, were studied at La Florida. Fieldwork was conducted during 6-7 December 2013, 29-31 October 2014, 16-18 November 2015, and 24-26 August 2016. The second site, Tarapoto (6˚28'08"S, 76˚21'13"W), is located on the Amazonian (eastern) side of the Andes Mountains at around 350 m a.s.l. and possesses a wet tropical forest. Phyllanthus acuminatus was studied at Tarapoto during 26-28 November 2013, 20-23 October 2014, and 21-22 November 2015. In addition to the above four woody Phyllanthus, three herbaceous Phyllanthus species were encountered during the course of the study; P. stipulatus and P. orbiculatus at Tarapoto, and P. amarus at a lowland Amazonian site at Iquitos (3˚34'00"S, 73˚07'11"W; ca. 100 m a.s.l.) visited during 29 August-2 September 2016. Pollination by Epicephala has never been found in herbaceous Phyllanthus in the Old World. However, because several herbaceous Phyllanthus species in Asia are associated with Epicephala that lack pollination behavior [12], the above three herbaceous species were also included in the study.
Phyllanthus salviifolius and P. huallagensis are members of the subgenus Xylophylla [14], a New World endemic group of ca. 90 species with its center of diversity in the Caribbean. Phyllanthus salviifolius belongs to the section Oxalistylis and is distributed in Costa Rica, Colombia, Venezuela, Ecuador, and Peru, whereas P. huallagensis belongs to the section Elutanthos and is only known from Peru [10]. Phyllanthus acuminatus and P. graveolens belong to the New World section Nothoclema of the subgenus Conami, which contains 10 species and ranges from Mexico to Argentina [17]. Both species are widely distributed from Mexico to the north to Peru (P. graveolens) and Argentina (P. acuminatus) to the south. Although Xylophylla and Nothoclema are not sister taxa, they group with other Neotropical herb, subshrub, and aquatic species and form the largest New World Phyllanthus radiation (Fig 1). Of the three herbaceous species studied, P. orbiculatus (sect. Apolepis) belongs to the same subgenus Conami as Nothoclema [18] and thus is likely a part of this large New World clade. On the other hand, P. amarus belong to the distantly related subgenus Swartziani [19], which represents an independent New World colonization (Fig 1). The phylogenetic position of P. stipulatus is presently uncertain.
All the four woody Phyllanthus species are found on forest edges or on disturbed land with abundant sunlight. Only P. salviifolius is a tree that reaches up to 10 m (Fig 2), whereas the containing Epicephala moth-pollinated plants are indicated in green, and the rest is colored blue. Lineages occurring in Asia/Oceania, Africa, and the New World are indicated by beige, turquoise, and yellow boxes, respectively. Although the number of Phyllanthus colonizations from the Old World to the New World depends on how the internal polytomy is resolved, suspected three colonization events are indicated on the tree. A group of entirely Madagascan species was recently placed in subgenus Gomphidium [27] and thus is tentatively labeled "Subg. Gomphidium (Madagascar)", but note that they are distinct from true Gomphidium in New Caledonia. Figure modified from [11].   (Figs 3 and 4). Phyllanthus salviifolius also differs from the other three species in that a single flowering branch either produces male or female flowers ( Fig 2C). The male flowers of P. salviifolius possess long pedicels and as many as 30 flowers aggregate on each axil (Fig 2D and 2E). The female flowers in turn are hardly pedicellate, and the tepals form a globular structure that covers the ovary and the style, leaving only the stigmatic surface exposed (Fig 2F). By contrast, both male and female flowers of P. acuminatus have spread tepals and exposed anthers and styles (Fig 3B and 3C). The flowers of P. graveolens and P. huallagensis, although belonging to different subgenera, resemble each other in that the tepals of both male and female flowers form a globe and almost entirely covers the anthers and the styles (Fig 4B, 4I and 4J). Once pollinated, the female flowers of P. huallagensis become erect until they mature into fruits and disperse the seeds (Fig 4H). Nectary discs are present in both male and female flowers of all four species.
The three herbaceous Phyllanthus species are common in sunny habitats along roadsides or on disturbed land and bear small, nectariferous male and female flowers (Fig 5)

Sampling and species delimitation of Epicephala moths
To determine whether the studied Phyllanthus species are associated with Epicephala, we initially inspected the fruits and the nearby foliage for the presence of Epicephala larvae and pupae. Because Epicephala moths were found in all the studied Phyllanthus, we sampled the fruits haphazardly in the field and incubated them at room temperature in plastic containers to rear the larvae. Adults that emerged were used for morphological examination and sequencing of the insect barcoding region to delimit species and assess host specificity. Morphological examinations follow standard dissection protocol detailed in [20]. In total, 91 adult pinned specimens were examined for the study, from which 28 genital dissections were made. The sensilla on the proboscis of females were also examined because they are an adaptation to facilitate active pollination and are reduced or lost in species that secondarily lost the pollination behavior [9]. Genomic DNA was extracted from 19 of the 28 specimens for which genital dissections were made, and the barcoding region of the cytochrome oxidase subunit I (COI) gene was sequenced using the LCO and HCO primers [21]. DNA extraction, polymerase chain reaction, and sequencing followed the protocols of [22]. The aligned sequence matrix of 612-bp length was subjected to a maximum-likelihood phylogenetic analysis on the IQ-TREE web server [23] using the default settings. Newly obtained sequences have been deposited in DDBJ under accession numbers LC424114-LC424132 and in BOLD under the project EPICE.

Behavioral observation
The behavior of Epicephala moths was studied in the field during 1800-2200 to determine whether any species is an active pollinator. We patrolled plant individuals with flowering branches at night using flashlights, and whenever Epicephala moths were found visiting female flower, we recorded whether each moth displayed pollination behavior prior to oviposition and the location of egg deposition. The moths were collected after observation, although some attempts to collect the moths were unsuccessful. The proboscises of the sampled moths were observed under a dissecting microscope for pollen load, and genital dissections were made to identify the species. field-collected female E. anomala (arrow) covered with Phyllanthus pollen; (i) a young fruit with Epicephala oviposition scars (arrows). Two front tepals have been artificially removed; (j) developed fruits, one of which having an exit hole (arrow) excavated by Epicephala larva. https://doi.org/10.1371/journal.pone.0210727.g002 In addition, non-Epicephala insects that visited the flowers were recorded and captured whenever possible. Each insect specimen was inspected under a dissecting microscope for pollen load to determine whether they could potentially contribute to pollination.

Pollen and egg loads on female flowers
Although direct observation of pollination behavior provides straightforward evidence that the species is an active pollinator, observation was not sufficient for Epicephala associated with P. graveolens and P. huallagensis. We therefore examined the female flowers of the two species for pollen and egg loads under a dissecting microscope. If the majority of the pollinated flowers are infested with moth eggs, and unpollinated flowers are free of moth eggs, it is likely that the associated Epicephala pollinates before oviposition and acts as the sole pollinator. In turn, if some fraction of pollinated flowers is free of moth eggs, co-pollinator may be present,  regardless of whether the associated Epicephala actively pollinates. We examined whether there is such an association between pollen and egg loads to compensate for a lack of direct observations in P. graveolens and P. huallagensis.

Phylogenetic positions of New World Epicephala
To infer the phylogenetic positions of New World Epicephala relative to the Old World species, we analyzed the sequences of the combined mitochondrial COI, nuclear elongation factor 1-alpha (EF1α) and arginine kinase (ArgK) genes. We used the primers and laboratory protocols described in [22] and [24] to obtain EF1αand ArgK sequences for one representative individual of each New World Epicephala species, chosen haphazardly from the individuals for which COI was sequenced as described. Obtained sequences were analyzed with published COI, EF1α, and ArgK sequence data for 29 Old World Epicephala and related Conopomorpha flueggella (associated with Flueggea). Sequences of Cuphodes diospyrosella, Stomphastis labyrinthica, and Melanocercops ficuvorella, obtained from the database, were used as outgroups. Phylogenetic analysis was done using IQ-TREE as described above for COI. Newly obtained EF1αand ArgK sequences have been deposited in DDBJ under accession numbers LC424133-LC424142.

Nomenclatural acts
The electronic edition of this article conforms to the requirements of the amended International Code of Zoological Nomenclature, and hence the new names contained herein are available under that Code from the electronic edition of this article. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix "http://zoobank.org/". The LSID for this publication is: urn:lsid:zoobank.org:pub:7B78433F-07E2-40ED-BAE1-C083AF3304C2. The electronic edition of this work was published in a journal with an ISSN, and has been archived and is available from the following digital repositories: PubMed Central, LOCKSS.

Species description
Morphological examination of the adults that emerged from the fruits of four woody and three herbaceous Phyllanthus resulted in recognition of five Epicephala species (Fig 6). Four of them were each specific to one of the four woody Phyllanthus hosts, whereas the fifth species was broadly associated with the three herbaceous species. Analysis of the COI sequences confirmed the existence of five distinct clades, corresponding to morphologically recognized species (S1 Fig). Intraspecific pairwise sequence variation was within the range of 0-0.16%, whereas pairwise sequence variation between species exceeded 2.7%.
Below we describe the five Epicephala species. Detailed description of morphology is provided in S1 Text.
Epicephala anomala Kawakita & Kato, sp. nov. urn:lsid:zoobank.org:act:171DA3E5-2318-4A01-90FD-5684CEA33F83 Diagnosis. This species and the following Epicephala acuminatella are unlike any other Epicephala species in having sclerotized blade on the posterior side of cucullus and elongated inward projection on dorsal margin of cucullus. This species can be clearly distinguished from E. acuminatella by the broader and overall straight shape of the sclerotized blade on cucullus and distinctly narrower lamella postvaginalis.
Description. Morphological description is provided in S1 Text. Diagnosis. This species is morphologically similar to E. nudilingua in having forked lamella postvaginalis but differs from the latter in lacking well developed cornutus and more rectangular sacculus.
Description. Morphological description is provided in S1 Text.

Adult Epicephala behavior and other floral visitors
The flowers of the four woody Phyllanthus species were not always available during our fieldwork, so the number of occasions on which we encountered adult Epicephala was limited. Nevertheless, we were able to successfully observe the behavior of three moths on each of P. salviifolius and P. acuminatus, one moth on P. graveolens, and two moths on P. amarus. We also observed one moth in the act of oviposition on P. huallagensis, but whether this moth pollinated the flower prior to oviposition is unclear. Below we provide details of the behavior of each moth species. A summary of the results is given in Table 1.
We encountered the flowering of P. salviifolius once in October 2014. There were numerous male flowers, but many female flowers had already been pollinated and started to develop into fruits. We observed three female individuals of E. anomala visiting such flowers with developing ovaries. After finding suitable female flower in which to oviposit, the moths bended the abdomen and inserted the ovipositor into the ovary through the interspace between the tepals or by penetrating the tepals directly with the ovipositor, without exhibiting pollination behavior ( Fig 2G; S1 Video). We observed more than 10 such oviposition events in each of two moths and three such ovipositions in one moth. Perplexingly, however, after capturing the Neotropical leafflower-leafflower moth mutualism three moths and inspecting their proboscises under a microscope, we found that their proboscises were coated with Phyllanthus pollen in a manner very similar to the proboscises of fieldcollected individuals of actively pollinating species. Thus, they have apparently visited the male flower before visiting female flowers and actively collected pollen. In addition, we observed one moth stretching the proboscis and inserting it into the flower several times before oviposition, which we regard as active pollination (S2 Video). This was observed in only one of >10 oviposition events by this moth, so active pollination occurred only occasionally in E. anomala.
No other flower visitors were observed except one thrips individual that was found on male flower during the daytime. The behavior of adult E. acuminatella on P. acuminatus was observed three times; twice in 2013 and once in 2014. Oviposition was observed twice in one moth and once each in the other two moths. On all occasions, the moths laid eggs in young fruits, but not female flowers, without exhibiting pollination behavior (Fig 3F). However, the two moths that were successfully captured both had their proboscises coated with Phyllanthus pollen, indicating that they had actively collected pollen before visiting female flowers. We collected one additional female that was resting on P. acuminatus foliage, and this individual also had pollen on the proboscis. Both male and female flowers of P. acuminatus were visited frequently by gall midges in the evening (Fig 3D and 3E). They pushed their mouthparts against the floral discs presumably to take in nectar and had many Phyllanthus pollen grains attached to their bodies (Fig 3D). No other flower visitors were found either during the daytime or in the evening. Gall midges were found resting on flowers or leaves of P. acuminatus during the daytime.
We studied the flower of P. graveolens in November 2015 and observed one adult Epicephala on female flower. Unlike E. anomala or E. acuminatella that laid eggs in young fruits, this Epicephala visited female flower, pollinated the stigma with the proboscis and subsequently laid an egg (Fig 4E). Nine pollen grains were attached to the stigma of this flower and one egg was laid internally on the ovary wall. We failed to capture this moth, but inspection of the photograph taken of this moth while resting on the branch shows that the proboscis was dusted with pollen ( Fig 4F). Thus, we consider this moth an active pollinator, similar to those typically found on Old World leafflowers. Because the moth was not captured, we could not confirm the species morphologically, but DNA barcoding of the egg indicated that the moth is E. graveolensella. In addition to Epicephala, thrips were commonly found inside both male and female flowers (Fig 4C and 4D). Both juvenile and adult thrips were found, indicating that they use P. graveolens flowers as brood sites. Pollen grains were attached invariably to 55 adult thrips individuals collected haphazardly on male flowers, and, out of 36 adult thrips individuals sampled on female flowers, two had pollen on their bodies, suggesting that thrips may act as co-pollinators.
On P. huallagensis, one moth was found in the act of oviposition (Fig 4K), but because this moth was the only individual that we could observe, we were unable to assess whether pollination takes place prior to oviposition. We also failed to capture this moth and thus could not inspect its proboscis microscopically, but the photograph shows that the proboscis is coated with pollen (Fig 4L). Thirty-one pollen grains were attached to the stigma of the flower visited by this moth, and one egg was laid internally on the ovary wall. Using DNA barcode, we confirmed that the moth is E. huellagensiella. No other flower visitors were found during the observation, although we found two thrips individual, without pollen, in one of 206 female flowers that we dissected.
Finally, two E. chancapiedra individuals were observed on P. amarus. Both individuals neither pollinated female flowers nor carried pollen on the proboscises, and laid eggs in young fruits (Fig 5G). Thus, this species is likely a non-pollinating parasite, similar to Epicephala associated with herbaceous Phyllanthus in the Old World. Ants and stingless bees were frequent visitors to P. amarus flowers, which likely contributed to pollination.

Proboscis morphology
The proboscises of the five Epicephala species were observed under a microscope to determine whether sensilla are present. The sensilla were clearly present on the proboscises of E. acuminatella, E. graveolensella, and E. huellagensiella, but absent in those of E. anomala and E. chancapiedra (Fig 7).

Pollen and egg loads on female flowers
Because behavioral observations were not sufficient for E. graveolensella and E. huallagensiella, we examined the female flowers of P. graveolens and P. huallagensis to determine whether there is association between pollination status and presence of moth eggs. In P. graveolens, we inspected 173 female flowers, of which 112 were pollinated. Out of the 112 pollinated flowers, only 64 (57.1%) received Epicephala eggs ( Table 2), indicating that co-pollinators, such as thrips, may be responsible for the pollination of the remaining flowers that had not received moth eggs. An alternative possibility is that Epicephala moths pollinated most of the flowers but failed to lay eggs in some of them (loss of eggs subsequent to oviposition is unlikely because moth ovipositions cause visible scars on ovaries which were not observed on flowers without eggs). We also examined 206 female flowers of P. huallagensis and found 154 that were pollinated. Of these, 130 (84.4%) had moth eggs (Table 2), so the contribution of co-pollinators, if any, is smaller than it is in P. graveolens. No moth egg was deposited on 61 and 52 unpollinated flowers of P. graveolens and P. huallagensis (Table 2).

Phylogenetic position of New World Epicephala
Maximum-likelihood analysis of the combined COI + EF1α+ ArgK gene sequences indicated that the four Epicephala species associated with woody Phyllanthus form a well-supported clade, and this clade is embedded among lineages of Old World active pollinators (Fig 8). In turn, E. chancapiedra grouped with Old World Epicephala species associated with herbaceous Phyllanthus (Fig 8). Because Old World Epicephala on herbaceous Phyllanthus all lack pollination behavior, the ancestor of E. chancapiedra likely did not possess the pollination behavior by the time it colonized the New World.

Discussion
Although the presence of Epicephala in the New World has been implicated based on the presence of Epicephala-like larvae and pupal cocoons on herbarium specimens of Neotropical Phyllanthus [25], this is the first report of any Epicephala from the New World. The diversity of Phyllanthus in Peru is not high as compared to other regions in the Neotropics; however, we found species-specific Epicephala species from each of four woody Phyllanthus that were studied and one Epicephala species associated with three herbaceous Phyllanthus. Considering that there are ca. 250 Phyllanthus species throughout the New World, there is probably a considerable diversity of Epicephala remaining to be found. Epicephala chancapiedra was associated with herbaceous Phyllanthus species belonging to two distantly related subgenera (Conami and Swartziani). This species is thus likely capable of attacking various herbaceous Phyllanthus species and may be found from other herbaceous Phyllanthus in other parts of the Neotropics.
Molecular phylogenetic analysis indicated that the four moth species associated with woody Phyllanthus are descendants of Old World active pollinators. We observed adult females carrying Phyllanthus pollen on the proboscises in all the four species, and pollination in at least two species (E. anomala and E. graveolensella). Sensilla on female proboscis were also confirmed in three species (E. acuminatella, E. graveolensella, and E. huallagensiella). These findings indicate that actively pollinating Epicephala moths, which originated in the Old World, successfully colonized the New World and remained as active pollinators as they diversified on New World Phyllanthus. It is unknown how Epicephala moths were able to colonize a remote continent, but a presumably young age of the genus (ca. 25 Ma [12]) suggests that colonization most likely occurred by means of transoceanic dispersal. Simultaneous dispersal of plants and moths (as larvae inside fruits) is unlikely because even if it did occur, emerged adult moths would not survive until the plants become mature enough to flower.
It is, however, not conclusive whether any Phyllanthus-Epicephala association in the New World is an obligate mutualism (Table 3). In P. graveolens and P. huallagensis, flowers that had moth eggs were always pollinated ( Table 2), suggesting either that the associated moths pollinate flowers before oviposition, or the moths are capable of distinguishing pollination status and selectively lay eggs in pollinated flowers without pollinating themselves. We consider that the former is more likely because we observed at least one E. graveolensella actively pollinate prior to oviposition. However, the P. graveolens-E. graveolensella association may not be obligate because 42.9% of pollinated flowers did not have moth eggs, indicating that co-pollinators may be present. Phyllathus huallagensis may be more dependent on Epicephala for pollination because there was a strong association between pollination status and egg load (Table 2), at least in the La Florida population during the period of our fieldwork. The imbricate tepals surrounding the anthers and styles in P. graveolens and P. huallagensis resemble those of Epicephala-pollinated Phyllanthus in the Old World, which hints at the possibility that their flowers are specialized for Epicephala pollination. It is also unknown whether there is net positive effect for the plant of being associated with Epicephala, because haphazard dissections of fruits with single exit holes indicated that a single moth larva consumes all the six seeds in each fruit in both P. graveolens and P. huallagensis. Such a pattern of destructive seed consumption is also the case for Epicephala-pollinated Phyllathus in New Caledonia, but moth mortality at the immature stage ensures that some seeds remain intact in this case [26]. In any case, actively pollinating Epicephala species likely contribute to the pollination of Phyllanthus in the New World, but to what extent Phyllanthus plants are dependent on Epicephala requires further ecological study.
We also observed the adult behaviors of E. anomala and E. acuminatella, but assessing whether they have positive effects on the reproduction of host Phyllanthus is not straightforward. Although both species laid eggs in young fruits, and thus most likely did not contribute to pollination, all the female moths that have been examined carried pollen on the proboscises, suggesting that they have the potential to act as pollinators. Because we observed one instance of E. anomala moth pollinating P. salviifolius flower (although the flower had been pollinated and started developing into fruit), one possibility is that E. anomala pollinates only occasionally. The majority of P. salviifolius female flowers that we observed during the study were already pollinated, but E. anomala may pollinate more frequently in situations where there are Neotropical leafflower-leafflower moth mutualism more virgin flowers, although this requires that the moth can discriminate between pollinated and unpollinated flowers. However, E. anomala lacks the sensilla on the proboscis entirely, which we regard as an indication that the species is evolving toward being parasitic or already is parasitic. The sensilla on the proboscis of E. acuminatella are also not well developed as compared to other actively pollinating species in Asia (Fig 7) [20], so selection to retain pollination behavior may be relaxed in this species as in E. anomala. Epicephala anomala and E. acuminatella are closely related on the phylogeny, and thus we hypothesize that there has been a reversal to a less mutualistic lifestyle in the common ancestor of the two species (Fig 8). We did not observe any alternative pollinator in P. salviifolius, but in P. acuminatus, gall midges may act as the primary pollinator.
Overall, the finding of Epicephala in the New World opens up a new avenue of research on the diversity and evolution of the leafflower-leafflower moth association. A large number of Epicephala species is likely to be found throughout the New World, especially in regions of high Phyllanthus diversity such as Cuba and Venezuela. Phyllanthus species in the sections Epistylium, occurring in the Caribbean, and Microglochidion, restricted to the tepuis of Guiana Highlands, have non-bifid and fused styles reminiscent of those of Glochidion in Asia; thus, obligate mutualistic relationships, as those found in the Old World, may be widespread in some regions or taxonomic groups. On the other hand, some species of New World Phyllanthus possess flowers that are most unusual of all Phyllanthus, such as P. orbicularis with large, white, showy tepals, or P. arbuscula with brightly red flowers borne on flattened, photosynthetic branches (phylloclades). These species likely have entirely different pollination systems, so it is of high interest to clarify how interactions with Epicephala and other pollinators have driven the evolution of floral diversity and led to the remarkable radiation of Phyllanthus in the New World. Blue lines indicate lineages with parasitic lifestyles, including species that either entirely lack the pollination behavior or show pollination behavior only occasionally [9,12]; green lines indicate lineages with active pollination behavior. Lineages occurring in Asia/Oceania, Africa, and the New World are indicated by beige, turquoise, and yellow boxes, respectively. Each terminal label includes information on host plant species. Abbreviations are: E., Epicephala; P., Phyllanthus; G., Glochidion; B., Breynia; F., Flueggea. Numbers at nodes are bootstrap probability values based on 1,000 replications. Major evolutionary events are indicated for selected nodes. Epicephala anomala and E. acuminatella are conservatively labeled as active pollinators, but there is a possibility that they are parasitic (see text for discussion).
https://doi.org/10.1371/journal.pone.0210727.g008  S2 Video. Female Epicephala anomala exhibiting active pollination behavior before attempting to oviposit into Phyllanthus salviifolius ovary. Ovipositor of this moth was blocked by the tepal, and oviposition was not successful. The female is the same individual as in S1 Video.