Oral sex is widely used in human foreplay, but rarely documented in other animals. Fellatio has been recorded in bonobos Pan paniscus, but even then functions largely as play behaviour among juvenile males. The short-nosed fruit bat Cynopterus sphinx exhibits resource defence polygyny and one sexually active male often roosts with groups of females in tents made from leaves. Female bats often lick their mate's penis during dorsoventral copulation. The female lowers her head to lick the shaft or the base of the male's penis but does not lick the glans penis which has already penetrated the vagina. Males never withdrew their penis when it was licked by the mating partner. A positive relationship exists between the length of time that the female licked the male's penis during copulation and the duration of copulation. Furthermore, mating pairs spent significantly more time in copulation if the female licked her mate's penis than if fellatio was absent. Males also show postcopulatory genital grooming after intromission. At present, we do not know why genital licking occurs, and we present four non-mutually exclusive hypotheses that may explain the function of fellatio in C. sphinx.
Citation: Tan M, Jones G, Zhu G, Ye J, Hong T, Zhou S, et al. (2009) Fellatio by Fruit Bats Prolongs Copulation Time. PLoS ONE 4(10): e7595. https://doi.org/10.1371/journal.pone.0007595
Editor: David Hosken, University of Exeter, United Kingdom
Received: July 20, 2009; Accepted: September 30, 2009; Published: October 28, 2009
Copyright: © 2009 Tan et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: Special Foundation for Young Scientists (200605) and Innovation Grant (CX2007) of Guangdong Province Academy of Science. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Although it is widely used in human foreplay, oral sex has rarely been recorded in non-human animals. Oral sex occurs infrequently between juvenile males or between juvenile females and juvenile males as play in bonobos Pan paniscus , . Hence, to date evidence for an adaptive explanation for oral sex in animals has been lacking, and the behaviour has been considered largely specific to humans, or associated with play. Here we provide evidence that oral sex by females on males (fellatio) is routine during copulation in short-nosed fruit bats Cynopterus sphinx (Chiroptera: Pteropodidae), and we argue that is likely to confer adaptive benefits.
Even though the bats (Chiroptera) belong to the second largest order of mammals (>1100 species ), little is known about their copulatory behavior because bats are nocturnal and many roosts are inaccessible to humans. At present, descriptions of copulatory behavior exists for the hammer-headed bat Hypsignathus monstrosus , the little brown bat Myotis lucifugus , the common vampire bat Desmodus rotundus , the Indian flying fox Pteropus giganteus , and the Brazilian free-tailed bat Tadarida brasiliensis , . Specialized behaviors associated with reproduction, including harem-forming, tent-making, and territorial defence appear during the breeding season in some bat species –.
The short-nosed fruit bat C. sphinx roosts in tents made from foliage that are constructed and defended by males to attract females as a form of resource defense polygyny . Moreover, the bats transport pollen and disperse the seeds of plants , and hence have great value in ecosystems. C. sphinx is listed as ‘Near Threatened’ in China, and almost meets the criteria for being considered ‘Vulnerable’ . Gopukumar & Balasingh discussed the mating strategy adopted by C. sphinx and the mechanics of tent-making . Some recent studies found that nonharem males were actively involving in female recruitment and also obtained some reproductive success , . Based on this information, we wanted to know more about the nature of copulation in this bat species. We observed that females were not passive during copulation but performed oral sex, licking their mate's penis during copulation. This paper will provide information on the copulatory behavior and the duration of copulations of C. sphinx under captive conditions, highlighting the possible functions of this unusual licking behavior.
Materials and Methods
The research presented in this manuscript was conducted according to protocols approved by the Guangdong Entomological Institute Administrative Panel on Laboratory Animal Care.
We conducted this study in January 2007 and from November 2007 to December 2007 in Guangzhou City (23°08′N, 113°15′E), Guangdong Province, southern China. The city experiences a south subtropical monsoon climate. Ornamental Chinese fan-palm trees are widespread in parks and on the university campus, and these are important roosting sites for C. sphinx –.
Bat capture and marking
We captured bats from Yuexiu Park (23°08′N, 113°15′E, 70 m a.s.l., 8 km from the laboratory) during daytime, and recorded the sex, age and reproductive state of all individuals. Subadults, pregnant females and lactating females were excluded from this research to avoid limiting the opportunities for copulation. Thirty males and thirty females were marked with split metal bat rings on their left (males) or right arms (females) and were held in thirty flight cages (2.9 m long ×2.4 m wide ×2.0 m in height) made of wire, with each cage holding a male and female that were paired at random. The flight cages were exposed to natural conditions and several leaves of Chinese fan-palm were hung on the ceilings of the cage to provide roosts for the bats. We changed the leaves at regular intervals. The bats were fed with bananas and water with added vitamin supplements ad libitum every day. During the study, the average humidity was 53.7±2.0% and average temperature was 20.2±0.5C (both mean±SE, N = 32). After the investigation, bats were released at the place of capture or used for other studies.
We observed behaviours at roosts by using a PICO2000 series multimedia digital video monitor connected to a computer. From 19.00 h to 07.00 h the next morning, we recorded behaviours continuously. In the early night, data were recorded directly by using scan sampling methods , with a 5 minute interval between scans. We also measured the frequency and duration of copulatory behaviours. The duration of copulation was defined as when the penis entered the vagina until when it withdrew completely. In the late night (from 24.00 h to 07.00 h), the PICO2000 series multimedia digital video monitoring system recorded the behaviours and transferred data to computers automatically for later analysis.
Twenty successful copulations were observed among these 30 pairs, and each copulation was from a different pair. We tested all data for normality, and used parametric analyses (Pearson correlation) and linear regression to determine whether the total length of time that the female licked the male's penis during copulation and the total duration of copulation were associated. Nonparametric tests (Mann-Whitney U test) were used when data were not distributed normally. Means are given with their standard error, and all tests were conducted at the 0.05 significance level.
During copulation, the pair appeared to move forwards and backwards uninterruptedly and rhythmically. When a male was chewing or severing the Chinese fan-palm leaves to make a tent, or when males crawled upon the upper surface of a tent or were grooming themselves within a tent, a female would fly to the tent, stretch her wings, move her head slowly towards the male, and then sniff the male's face and neck. Subsequently, the pair's heads extended towards each other and the bats would lick one another. At this time, the male would make approaches to the female with his thumbs. After moving onto the female's back, the male would adjust his position to find a more appropriate copulatory posture, so that the pair would adopt a face-to-back mating posture. Sometimes the female appeared to resist, or even escaped by accident, and then the male would follow her until copulation was completed. In two instances, the female evaded the male for about eight to 25 seconds and turned to bite the male, but later the male followed her until mating was completed. In four instances, the female appeared to resist the male's approaches, but did not evade successfully, and copulations were eventually completed. During the copulation, the male usually maintained a tight hold on the scruff of the female's neck by using his mouth, and his thumbs held her wings firmly. When copulation was completed, the male licked his penis for several seconds. This self-licking occurred after all of 20 copulations, but was absent after three instances in which intromission failed to occur. Subsequently, the male often groomed himself or licked the inner surface of the tent, yet seldom flew away. Also, the female groomed herself and typically stayed close to her mate.
Interestingly, we found that the female lowered her head to lick the shaft or the base of male penis frequently during copulation (Video S1). The male never withdrew when his penis was licked by the female. Genital licking was observed in 14 of 20 copulations, whereas six copulations did not involve licking behavior (Fig. 1). The average duration of penis licking was 19.14±3.45 s, representing about 8.7% of the average duration of copulation (220.29±26.19 s (N = 14)). There was a strong correlation between the total length of time that the female licked the male's penis and the duration of copulation (Pearson correlation: r12 = 0.828, P<0.001: Fig. 2). Therefore the longer the female licked the penis of her mate, the longer they copulated for. Furthermore, we found that whether a female licked her mate's penis during copulation had a significant influence on the duration of copulation. The pairs spent more time copulating if the female licked her mate's penis (220.29±26.19 sc, N = 14) than on occasions when females did not show licking behavior (121.83±20.56 s, N = 6: Mann-Whitney U test: P = 0.039; Fig. 3). This result suggests that the licking behaviour may play an important role in copulation by prolonging intromission.
The relationship is described by the equation: duration of copulation (s) = 101.24+6.22 (duration of licking behaviour, (s)) (F 1,13 = 26.14, P<0.001). Therefore each second of licking prolongs copulation by approximately 6 s.
We found that female short-nosed fruit bats C. sphinx lick their mate's penis regularly during copulation, and that each second of licking results in approximately 6 extra seconds of copulation. Copulations also last longer if licking occurs than when no licking takes place. Our observations are the first to show regular fellatio in adult animals other than humans.
The duration of copulation in C. sphinx (100–300 s) is much longer than in the Indian flying fox P. giganteus (30–40 s), and the hammer-headed bat H. monstrosus (30–60 s) , . The Indian flying fox and the hammer-headed bat were studied in the field however, and male-male competition in colonies may reduce copulation time. Bats may also shorten copulation time to reduce predation risk in the field, especially if vigilance is reduced during copulation.
Our observations showed that the female frequently lowered her head to only lick the penile shaft during intromission, because the glans penis has already entered the vagina. In six instances licking behavior was not apparent, maybe because the female was forced to copulate and sometimes evaded successfully for several seconds. There are few observations of fellatio in non-human animals. Oral sex was found as a play behaviour between juvenile males or between juvenile female and juvenile male bonobos Pan paniscus , . Schürmann observed that a female orangutan, Pongo pygmaeus, often interrupted copulation for a short while, manipulating her mate's penis with her hand, licking it or putting it in her mouth before mounting again. It is plausible that this female's behavior increased male arousal . In general, many animals may lick genitals before and after copulation, for example, the male of ring-tailed lemur, Lemur catta, often licks the genitals of the female in order to judge whether she is in oestrous, and after copulation, he also licks his penis . Both male and female Livingstone's fruit bats (Pteropus livingstonii) also licked the genitals of their partners during heterosexual interactions , . However, because of the limited details provided, we do not know whether fellatio occurs during copulation in these species. The bat penis contains erectile tissue (corpus cavernosa and corpus spongiosum) which is similar to that found in primates and humans. If the erectile tissue is stimulated during copulation e.g. by rhythmic vaginal contraction, it will increase the rigidity of the penis, and maintain the erection for longer . We speculate that the female C. sphinx licks the male penis to increase penile stimulation, stiffening the penis and maintaining the male's erection. At the same time, the female's saliva may increase lubrication, thus facilitating intromission and thrusting. In combination, these features may prolong copulation in C. sphinx.
So in a similar way to the anthropoid primates , the C. sphinx females (like most animals, see ) are not passive during copulation but rather communicate with the male, in this case by licking his penis. We propose a series of adaptive hypotheses to explain genital licking in C. sphinx. First, genital licking may lubricate the penis or increase penile stimulation, prolonging the duration of copulation. Prolonged copulation might assist sperm transport from the vagina to the oviduct, or stimulate secretions of the pituitary gland in the female  and hence increase the likelihood of fertilization. Second, prolonged copulation might be a method of mate-guarding, because the mates would normally segregate after copulation to form unisexual groups which persist throughout the non-breeding season . Third, fellatio may confer bactericidal benefits and assist in the prevention of sexually transmitted diseases (STDs) both to females –, and to males that lick their own penis briefly after copulation –. Saliva has a protective repertoire that goes beyond antibacterial activity to include antifungal, antichlamydial, and antiviral properties as well . Finally, genital licking may facilitate the detection and identification of MHC-dependent chemical cues associated with mate choice , .
In conclusion, we have documented fellatio in animals that may have functional significance. Of course, adaptive benefits remain unproven until tested, ideally by experimentation, but our study identifies potential avenues to explore if the null hypothesis of no benefit (e.g. via low cost to donor and recipient) is to be rejected. We believe that ours is the first large scale observational study of oral sex in non-humans, and we extend the interpretation of such behaviour beyond that of ‘pleasure giving’ into an evolutionary context. Importantly we show that fellatio increases the duration of copulation. This may have several important functions, for example increasing fertilization success, or even reducing the risk of contracting STDs. The behaviour presumably favours the donor, although it may also benefit both partners especially if fertilization success is increased. It is conceivable that the female manipulates the male by increasing sexual stimulation, so that she ultimately benefits.
We thank Guangpeng Wang (Shanghai Entry-Exit Inspection and Quarantine Bureau), Qian Yao (Institute of Zoology, Chinese Academy of Sciences), Dewei Li (Hainan Normal University), and Dongmei Yu (Guangdong Entomological Institute) for assistance during observations. We also thank Aleksei Chmura (Consortium for Conservation Medicine, CCM) and Quansheng Liu (Guangdong Entomological Institute) for useful help in the data analysis. We are grateful to Jinshuo Zhang (Institute of Zoology, Chinese Academy of Sciences) and Charles Nunn (Harvard University) for discussion.
Conceived and designed the experiments: SZ SZ LZ. Performed the experiments: MT GZ JY TH LZ. Analyzed the data: MT GJ LZ. Wrote the paper: MT GJ GZ SZ LZ.
- 1. De Waal FBM (1995) Bonobo sex and society: the behavior of a close relative challenges assumptions about male supremacy in human evolution. Sci Am 272: 82–88.FBM De Waal1995Bonobo sex and society: the behavior of a close relative challenges assumptions about male supremacy in human evolution.Sci Am2728288
- 2. Palagi E, Paoli T, Tarli SB (2004) Reconciliation and consolation in captive bonobos (Pan paniscus). Am J Primatol 62: 15–30.E. PalagiT. PaoliSB Tarli2004Reconciliation and consolation in captive bonobos (Pan paniscus).Am J Primatol621530
- 3. Simmons NB (2005) Order Chiroptera. In: Wilson DE, Reeder DM, editors. Mammal species of the world: a taxonomic and geographic reference, 3rd edition. Baltimore: The Johns Hopkins University Press. pp. 312–525.NB Simmons2005Order Chiroptera.DE WilsonDM ReederMammal species of the world: a taxonomic and geographic reference, 3rd editionBaltimoreThe Johns Hopkins University Press312525
- 4. Bradbury JW (1977) Lek mating behavior in the hammer-headed bat. Z Tierpsychol 45: 225–255.JW Bradbury1977Lek mating behavior in the hammer-headed bat.Z Tierpsychol45225255
- 5. Thomas DW, Fenton MB, Barclay RMR (1979) Social behavior of the little brown bat, Myotis lucifugus. I. Mating behavior. Behav Ecol Sociobiol 6: 129–136.DW ThomasMB FentonRMR Barclay1979Social behavior of the little brown bat, Myotis lucifugus. I. Mating behavior.Behav Ecol Sociobiol6129136
- 6. Wilkinson GS (1985) The social organization of the common vampire bat. II. Mating system, genetic structure, and relatedness. Behav Ecol Sociobiol 17: 123–134.GS Wilkinson1985The social organization of the common vampire bat. II. Mating system, genetic structure, and relatedness.Behav Ecol Sociobiol17123134
- 7. Koilraj BJ, Agoramoorthy G, Marimuthu G (2001) Copulatory behaviour of Indian flying fox Pteropus giganteus. Curr Sci 80: 15–16.BJ KoilrajG. AgoramoorthyG. Marimuthu2001Copulatory behaviour of Indian flying fox Pteropus giganteus.Curr Sci801516
- 8. French B, Lollar A (1998) Observations on the reproductive behavior of captive Tadarida brasiliensis mexicana (Chiroptera: Molossidae). Southwest Nat 43: 484–490.B. FrenchA. Lollar1998Observations on the reproductive behavior of captive Tadarida brasiliensis mexicana (Chiroptera: Molossidae).Southwest Nat43484490
- 9. Keeley ATH, Keeley BW (2004) The mating system of Tadarida brasiliensis (Chiroptera: Molossidae) in a large highway bridge colony. J Mamm 85: 113–119.ATH KeeleyBW Keeley2004The mating system of Tadarida brasiliensis (Chiroptera: Molossidae) in a large highway bridge colony.J Mamm85113119
- 10. Neuweiler G (2000) The biology of bats. New York: Oxford University Press. 310 p.G. Neuweiler2000The biology of bats.New YorkOxford University Press310
- 11. McCracken GF, Wilkinson GS (2000) Bat mating systems. In: Crichton EG, Krutzsch PH, editors. Reproductive biology of bats. San Diego: Academic Press. pp. 321–360.GF McCrackenGS Wilkinson2000Bat mating systems.EG CrichtonPH KrutzschReproductive biology of batsSan DiegoAcademic Press321360
- 12. Gopukumar N, Balasingh J (2002) Nature watch: tent-making bats. J Sci Edu 6: 63–67.N. GopukumarJ. Balasingh2002Nature watch: tent-making bats.J Sci Edu66367
- 13. Balasingh J, Koilraj J, Kunz TK (1995) Tent construction by the short-nosed fruit bat Cynopterus sphinx (Chiroptera: Pteropodidae) in Southern India. Ethology 100: 210–229.J. BalasinghJ. KoilrajTK Kunz1995Tent construction by the short-nosed fruit bat Cynopterus sphinx (Chiroptera: Pteropodidae) in Southern India.Ethology100210229
- 14. Nathan PT, Raghuram H, Elangovan V, Karuppudurai T, Marimuthu G (2005) Bat pollination of kapok tree, Ceiba pentandra. Curr Sci 88: 1679–1681.PT NathanH. RaghuramV. ElangovanT. KaruppuduraiG. Marimuthu2005Bat pollination of kapok tree, Ceiba pentandra.Curr Sci8816791681
- 15. Wang S, Xie Y (2004) China species red list, vol. 1. Beijing: Higher Education Press. 288 p.S. WangY. Xie2004China species red list, vol. 1.BeijingHigher Education Press288
- 16. Gopukumar N, Karuppudurai T, Nathan PT, Sripathi K, Arivarignan G, et al. (2005) Solitary adult males in a polygynous-mating bat (Cynopterus sphinx): a forced option or a strategy? J Mamm 86: 281–286.N. GopukumarT. KaruppuduraiPT NathanK. SripathiG. Arivarignan2005Solitary adult males in a polygynous-mating bat (Cynopterus sphinx): a forced option or a strategy?J Mamm86281286
- 17. Karuppudurai T, Sripathi K, Gopukumar N, Elangovanc V, Arivarign G (2007) Transition of nonharem male to harem male status in the short-nosed fruit bat Cynopterus sphinx. Mamm Biol 73: 138–146.T. KaruppuduraiK. SripathiN. GopukumarV. ElangovancG. Arivarign2007Transition of nonharem male to harem male status in the short-nosed fruit bat Cynopterus sphinx.Mamm Biol73138146
- 18. Corlett RT (2005) Interactions between birds, fruit bats and exotic plants in urban Hong Kong, South China. Urban Ecosys 8: 275–283.RT Corlett2005Interactions between birds, fruit bats and exotic plants in urban Hong Kong, South China.Urban Ecosys8275283
- 19. Chan CSM, Shek CT (2006) Survey on the Short-nosed Fruit Bat (Cynopterus sphinx) in the urban areas of Hong Kong. HK Biodivers 11: 8–10.CSM ChanCT Shek2006Survey on the Short-nosed Fruit Bat (Cynopterus sphinx) in the urban areas of Hong Kong.HK Biodivers11810
- 20. Zhang W, Zhou SY, Zhu GJ, Chen QM, Huang JR, et al. (2008) Habitat selection of Cynopterus sphinx angulatus in Guangzhou City. Chinese J Ecol 27: 286–289.W. ZhangSY ZhouGJ ZhuQM ChenJR Huang2008Habitat selection of Cynopterus sphinx angulatus in Guangzhou City.Chinese J Ecol27286289
- 21. Martin P, Bateson P (2007) Measuring behavior: An introductory guide. 2nd ed. Cambridge: Cambridge University Press. 176 p.P. MartinP. Bateson2007Measuring behavior: An introductory guide. 2nd ed.CambridgeCambridge University Press176
- 22. Schürmann C (1982) Mating behaviour of wild orangutans. In: Boer LEM, editor. The orangutan, its biology and conservation. The Hague: Junk. pp. 269–284.C. Schürmann1982Mating behaviour of wild orangutans.LEM BoerThe orangutan, its biology and conservationThe HagueJunk269284
- 23. Koyama N (1988) Mating behavior of ring-tailed lemurs (Lemur catta) at Berenty, Madagascar. Primates 29: 163–175.N. Koyama1988Mating behavior of ring-tailed lemurs (Lemur catta) at Berenty, Madagascar.Primates29163175
- 24. Bagemihl B (1999) Biological exuberance: animal homosexuality and natural diversity. New York: St. Martin's Press. 752 p.B. Bagemihl1999Biological exuberance: animal homosexuality and natural diversity.New YorkSt. Martin's Press752
- 25. Smith SJ, Leslie DM Jr (2006) Pteropus livingstonii. Mammal Spec 792: 1–5.SJ SmithDM Leslie Jr2006Pteropus livingstonii.Mammal Spec79215
- 26. Neuweiler G (2000) The biology of bats. New York: Oxford University Press. G. Neuweiler2000The biology of bats.New YorkOxford University Press
- 27. Reeder DM (2003) The potential for cryptic female choice in primates: behavioral, anatomical, and physiological considerations. In: Jones CB, editor. Sexual selection and reproductive competition in primates: new perspectives and directions. Norman: American Society of Primatologists. pp. 255–303.DM Reeder2003The potential for cryptic female choice in primates: behavioral, anatomical, and physiological considerations.CB JonesSexual selection and reproductive competition in primates: new perspectives and directionsNormanAmerican Society of Primatologists255303
- 28. Eberhard WG (1996) Female control: sexual selection by cryptic female choice. Princeton, New Jersey: Princeton University Press. 472 p.WG Eberhard1996Female control: sexual selection by cryptic female choice.Princeton, New JerseyPrinceton University Press472
- 29. Bates PJJ, Harrison DL (1997) Bats of the Indian subcontinent. Sevenoaks, England: Harrison Zoological Museum. 258 p.PJJ BatesDL Harrison1997Bats of the Indian subcontinent.Sevenoaks, EnglandHarrison Zoological Museum258
- 30. Baron S, Singh I, Chopra A, Coppenhaver D, Pan JZ (2000) Innate antiviral defenses in body fluids and tissues. Antivir Res 48: 71–89.S. BaronI. SinghA. ChopraD. CoppenhaverJZ Pan2000Innate antiviral defenses in body fluids and tissues.Antivir Res487189
- 31. Lockhart AB, Thrall PH, Antonovics J (1996) Sexually transmitted diseases in animals: ecological and evolutionary implications. Biol Rev 71: 415–471.AB LockhartPH ThrallJ. Antonovics1996Sexually transmitted diseases in animals: ecological and evolutionary implications.Biol Rev71415471
- 32. Canfield PJ, Love DN, Mearns G, Farram E (1991) Chlamydial infection in a colony of captive koalas. Australian.Vet J 68: 167–169.PJ CanfieldDN LoveG. MearnsE. Farram1991Chlamydial infection in a colony of captive koalas.Australian.Vet J68167169
- 33. Thrall PH, Antonovics J, Dobson AP (2000) Sexually transmitted diseases in polygynous mating systems: prevalence and impact on reproductive success. Proc R Soc Lond B 267: 1555–1563.PH ThrallJ. AntonovicsAP Dobson2000Sexually transmitted diseases in polygynous mating systems: prevalence and impact on reproductive success.Proc R Soc Lond B26715551563
- 34. Hart BL, Korinek E, Brennan P (1987) Postcopulatory genital grooming in male rats: Prevention of sexually transmitted infections. Physiol Behav 41: 321–325.BL HartE. KorinekP. Brennan1987Postcopulatory genital grooming in male rats: Prevention of sexually transmitted infections.Physiol Behav41321325
- 35. Morga FJ, Trujillo AO (2001) Frecuencia del lamido poscopulatorio del pene en machos cabríos (Capra hircus) y posible función. Vet Méx 32: 301–303.FJ MorgaAO Trujillo2001Frecuencia del lamido poscopulatorio del pene en machos cabríos (Capra hircus) y posible función.Vet Méx32301303
- 36. Nie YG, Hu JC, Chen FH, Liu T (2006) Courtship and mating behaviors of Anourosorex squamipes. J China W Nor Uni (Nat Sci) 27: 86–89.YG NieJC HuFH ChenT. Liu2006Courtship and mating behaviors of Anourosorex squamipes.J China W Nor Uni (Nat Sci)278689
- 37. Jia ZY, Jiang ZG, Wang ZW (2000) Observation on the behaviors of masked palm civet in reproductive season. Acta Theriol 20: 108–115.ZY JiaZG JiangZW Wang2000Observation on the behaviors of masked palm civet in reproductive season.Acta Theriol20108115
- 38. Mandel ID (1993) A contemporary view of salivary research. Crit Rev Oral Biol M 4: 599–604.ID Mandel1993A contemporary view of salivary research.Crit Rev Oral Biol M4599604
- 39. Mayer F, Brunner A (2007) Non-neutral evolution of the major histocompatibility complex class II gene DRB1 in the sac-winged bat Saccopteryx bilineata. Nature 99: 257–264.F. MayerA. Brunner2007Non-neutral evolution of the major histocompatibility complex class II gene DRB1 in the sac-winged bat Saccopteryx bilineata.Nature99257264
- 40. Wedekind C, Seebeck T, Bettens F, Paepke AJ (1995) MHC-dependent mate preferences in humans. Proc R Soc Lond B 260: 245–249.C. WedekindT. SeebeckF. BettensAJ Paepke1995MHC-dependent mate preferences in humans.Proc R Soc Lond B260245249