Fig 1.
A–Bosellia mimetica, specimen length: ~5mm (when stretched out as pictured here). B–Elysia marcusi, specimen length: ~4mm (when stretched out rather than disk-shaped as seen here). C–Elysia tuca, specimen length: ~7mm. D–Elysia papillosa, specimen length: ~8mm. E–Elysia cornigera, specimen length: ~7mm. F–Elysia timida, specimen length: ~8mm. G–Ercolania fuscata, specimen length: ~3mm. H–Ercolania viridis (both color morphs found in Florida), specimen length: ~3-4mm. I–Placida dendritica, specimen length: ~4mm. J–Elysia patina, specimen length: ~6mm. Photo by Gregor Christa, used with permission. K–Thuridilla hopei, specimen length: ~8mm.
Table 1.
Specimen collection information.
Table 2.
Overview of each experiment detailing the number and age of the juvenile El. timida used in this study.
Parentheses refer to animals that were included at the beginning of the experiment and placed in starvation, but did not survive until the date they were to be surveyed. They are listed here for clarity even though they did not survive long enough to be used in the experiments and were therefore excluded from all analyses. DPM–Days post-metamorphosis.
Fig 2.
The number of deaths per day in starvation.
Individuals from each age group (4, 10, 15, 25 DPM) were monitored each day until death. 4 DPM deaths are indicated in grey, 10 DPM deaths in light blue, 15 DPM in dark blue and 25 DPM in green. The relatively even distribution suggests a range of fitness levels amongst specimens of each age. The large gap depicts the differences between the younger time points (4, 10, 15) where functional kleptoplasty is not occurring and the 25 DPM juveniles where short-term retention has been developed.
Fig 3.
Confocal microscopy images of juvenile El. timida and their chlorophyll a content during starvation.
A– 4 DPM juvenile before starvation (day 0). B–The same 4 DPM juvenile after 1 day of starvation. C–The same 4 DPM juvenile after 2 days of starvation. D– 10 DPM juvenile before starvation (day 0). E–The same 10 DPM juvenile after 2 days of starvation. F–The same 10 DPM juvenile after 4 days of starvation. G– 15 DPM juvenile before starvation (day 0). H–The same 15 DPM juvenile after 3 days of starvation. I–The same 15 DPM juvenile after 5 days of starvation. J– 25 DPM juvenile before starvation (day 0). K–The same 25 DPM juvenile after 8 days of starvation. L–The same 25 DPM juvenile after 16 days of starvation. Scale bars: A-C 70μm; D-F 250μm; G-I 350μm, J-L: 450μm.
Fig 4.
Functional chloroplast abundance during starvation for each age group (DPM).
The average juvenile longevity is shown by the black dotted lines. A–Each juvenile El. timida (n = 10), aged 4 days post-metamorphosis (DPM) was measured daily to determine the decrease in functional chloroplast abundance throughout the starvation period until death. The green star indicates an animal that died within the first 24 hours and could not be represented by a line. B–The longevity of each juvenile El. timida specimen aged 10 DPM (n = 10). The green and blue stars indicate individual animals that died within the first 24 hours and could not be represented by a line. C– 15 DPM juvenile longevities in starvation (n = 10). D– 25 DPM individual longevities in starvation (n = 10). E–The average chloroplast abundance for each age group depicted in A-D, plotted together for comparison with the same axes scaling. F–Functional chloroplast abundance in starved and starved then reintroduced to food El. timida juveniles of each age group for each time point surveyed. Juveniles of each age group were starved and their functional chloroplast abundances recorded at 0, 3, 7, 10, 15 and 25 in starvation. Additional animals were re-introduced to food and allowed to feed for 2 hours before their chloroplast abundances were recorded. 4 DPM juveniles are indicated by diamonds: red for starved and pink for starved-then-fed; 10 DPM juveniles are shown by circles: purple for starved and lavender for starved-then-fed; 15 DPM juveniles are denoted by squares, dark blue for starved and light blue for starved-then-fed; 25 DPM juveniles are designated with triangles: dark green for starved and light green for starved-then-fed.
Fig 5.
Digestive activity as indicated by chloroplast and lysosome abundance in specimens of 4, 10, 15 and 25 Days Post-Metamorphosis (DPM) El. timida.
Black shapes indicate starved animals and grey shapes indicate starved-then-fed animals. Diamonds show chloroplast abundance inside the digestive gland tubule, here referred to as the region of interest (ROI), triangles denote lysosome abundance inside the ROI and circles depict lysosome abundance outside the ROI. All values are given in percent coverage, the percentage of tissue either inside or outside the ROI where fluorescent signal was measured as compared to the total area covered by the tissue. Overlapping shapes were illustrated directly next to each other for clarity, but were measured on the same day. A–digestive activity in 4 DPM juveniles. B– 10 DPM juveniles. C– 15 DPM juveniles. D– 25 DPM juveniles.
Fig 6.
Longevity in starvation by species.
A-E–The x-axis shows the individual specimen number and the y-axis records the number of days that specimen survived. The black dotted and dashed lines show the respective averages for each species and the grey bars indicate one standard deviation to each side of the mean. A–Ercolania viridis is denoted by triangles and Ercolania fuscata by circles. The Er. viridis average was 5.8 ± 1.1 days (dotted line) and Er. fuscata averaged 7.25 ± 1.7 (dashed line). B–Placida dendritica is represented by triangles and Elysia tuca by circles. The P. dendritica average was 8.85 ± 1.3 days (dotted line) and El. tuca averaged 13.35 ± 1.9 (dashed line). C–Elysia marcusi is signified by triangles and Bosellia mimetica by circles. The El. marcusi average was 4.55 ± 0.89 days (dotted line) and B. mimetica averaged 13.65 ± 1.4 (dashed line). D–Elysia patina is conveyed by triangles and Elysia cornigera by circles. The El. patina average was 6.15 ± 1.7 days (dotted line) and El. cornigera averaged 22.15 ± 2.3 (dashed line). E–Elysia papillosa is designated by triangles and Thuridilla hopei by circles. The El. papillosa average was 22.1 ± 1.3 days (dotted line) and T. hopei averaged 23.55 ± 1.8 (dashed line). F–All of the short- and non-retaining species average longevities in starvation and the El. timida juveniles average longevities are depicted, showing the clear difference in juvenile longevities and grouping within either the short-term retention slugs and non-retaining slugs. Circles depict Non-Retaining slug species (NR); squares indicate Short-term Retaining (StR) species and triangles show the different El. timida juvenile age groups.
Fig 7.
Pulse Amplitude Modulated (PAM) fluorometry values for a range of short-term retention and non-retaining species during starvation.
A–The PAM values for Placida dendritica are indicated by light grey circles, Elysia marcusi by black triangles and Ercolania fuscata by dark grey squares. P. dendritica is best modeled by the function y = 4.22x2–103.95x + 610.26 (R2 = 0.97), El. marcusi by y = -15.17x2 + 21.83x + 441 (R2 = 0.92) and El. fuscata by y = -1.59x3 + 28.87x2–169.65x + 320.76 (R2 = 0.98). B–The PAM values for Ercolania viridis are indicated by grey circles and Elysia tuca by black triangles. Er. viridis is best modeled by the function y = -5.14x3 + 63.87x2–248.13x + 296 (R2 = 0.95) and El. tuca by y = 1.14x2–40.43x + 507.49 (R2 = 0.91). C–The PAM values for Elysia papillosa are indicated by dark grey squares, Elysia patina by black circles and Thuridilla hopei by light grey triangles. El. papillosa is best modeled by the function y = -0.55x2–7.54x + 514.6 (R2 = 0.94), El. patina by y = -35.59x + 660.95 (R2 = 0.89) and T. hopei by y = 1.48x2–60.38x + 577.04 (R2 = 0.98). D–The PAM values for Elysia cornigera are indicated by grey circles and Bosellia mimetica by black triangles. El. cornigera is best modeled by the function y = 1.91x2–74.94x + 718.98 (R2 = 0.97) and B. mimetica by y = 1.26x2–62.16x + 615.03 (R2 = 0.97)The error bars show the standard error.