Fig 1.
Dorsal views, anterior up, of adult H. robusta, H. austinensis and H.octatestisaca, respectively, highlighting differences in body wall pigmentation. A) This specimen had fed recently on an artificial food source containing Fast Green dye, which clearly outlines four of the five pairs of large anterior midgut lobes (caecae, long arrows), along with the four pairs of smaller intestinal lobes (arrowheads), and the rectum (short arrow). B) In this animal, which had fed on bloodworms, the crop caecae are labeled red; the central annulus in each segment contains prominent white and brown pigment patches. C) In common with other H. stagnalis-like species, this animal bears a chitinous scute (arrow) on the dorsal anterior surface.
Table 1.
Clutch size data for self-fertilizing and interbreeding cohorts of Helobdella spp.
Table 2.
Clutch interval data for self-fertilizing and interbreeding cohorts of Helobdella spp.
Fig 2.
Reproduction in an interbreeding cohort of 23 H. austinensis.
A) Cohort survival (blue, left axis) and aggregate clutch production (orange, right axis) as a function of time, for a cohort of animals fed ad lib on bloodworms. B) Aggregate embryo production (red, left axis); black dots indicate the size (number of embryos, right axis) and deposition date of each individual clutch. C) The same data as in B, except the estimated (EST) assignments of clutches into first, second and third layings are indicated by coloring dots as indicated (see text for details). 95% confidence intervals for the timing and clutch size of the inferred clusters of reproductive activity are: 100 to 118 days and 76 to 112 embryos for cluster 1; 169 to 208 days and 68 to 107 embryos for cluster 2.
Fig 3.
Reproduction in an interbreeding cohort of 60 H. austinensis.
A) Cohort survival (blue, left axis) and aggregate clutch production (orange, right axis) as a function of time, for a cohort of animals fed ad lib on bloodworms. B) Aggregate embryo production (red, left axis); black dots indicate the size (number of embryos, right axis) and deposition date of each individual clutch. C) The same data as in B, except the estimated (EST) assignments of clutches into first, second and third layings are indicated by coloring dots as indicated (see text for details). 95% confidence intervals for the timing and clutch size of the inferred clusters of reproductive activity are: 107 to 115 days and 39 to 48 embryos for cluster 1; 211 to 217 days and 35 to 47 embryos for cluster 2; 269 to 293 days and 30 to 48 embryos for cluster 3.
Fig 4.
An interbreeding cohort of 48 H. robusta exhibits clustered bouts of reproduction.
A) Cohort survival (blue, left axis) and aggregate clutch production (orange, right axis) as a function of time, for a cohort of animals fed ad lib on snails. B) Aggregate embryo production (red, left axis); black dots indicate the size (number of embryos, right axis) and deposition date of each individual clutch. C) The same data as in B, except the estimated (EST) assignments of clutches into first, second and third layings are indicated by coloring dots as indicated (see text for details). 95% confidence intervals for the timing and clutch size of the inferred clusters of reproductive activity are: 104 to 110 days and 21 to 27 embryos for cluster 1; 143 to 151 days and 40 to 51 embryos for cluster 2; 180 to 189 days and 61 to 73 embryos for cluster 3; 216 to 226 days and 68 to 83 embryos for cluster 4; 248 to 258 days and 43 to 63 embryos for cluster 5.
Fig 5.
Bar graph showing the distribution of clutch deposition.
Clutch deposition events occurring within five day bins, for the experiments shown in Figs 2, 3, 4 and 6.
Fig 6.
Clustered reproductive activity by a H. robusta cohort is not observed in a “pseudo-cohort”.
The pseudo cohort was generated by combining the reproductive parameters observed for isolated individuals. A-C) A pseudo-cohort was created by graphing the aggregated data from 16 animals reared in isolation. 95% confidence intervals for the timing and clutch size of the inferred clusters of reproductive activity are: 56 to 70 days and 24 to 45 embryos for cluster 1; 93 to 101 days and 47 to 70 embryos for cluster 2; 122 to 134 days and 65 to 84 embryos for cluster 3; 158 to 177 days and 59 to 86 embryos for cluster 4; 199 to 219 days and 29 to 71 embryos for cluster 5; 223 to 304 days and 0 to 71 embryos for cluster 6. D) For comparison, the actual clutch groupings are denoted using the same color scheme. 95% confidence intervals for the timing and clutch size of the actual clusters of reproductive activity are: 49 to 61 days and 18 to 23 embryos for cluster 1; 79 to 88 days and 42 to 62 embryos for cluster 2; 102 to 113 days and 60 to 80 embryos for cluster 3; 131 to 143 days and 65 to 90 embryos for cluster 4; 160 to 181 days and 54 to 84 embryos for cluster 5; 187 to 212 days and 29 to 73 embryos for cluster 6; 216 to 271 days and 19 to 69 embryos for cluster 7. Note that the inference procedure misassigned some clutches, and that only six rounds of reproduction were inferred, whereas the true value was eight.
Fig 7.
Monte Carlo simulations of reproductive activity in H. robusta.
A, B) Simulated reproductivity of 16 and 48 animals, respectively, using parameters from 16 self-fertilizing animals raised in isolation. C, D) Simulation of 16 and 48 animals, respectively, using parameters inferred from the cohort of 48 interbreeding animals. Note that none of these simulations capture the temporal clustering observed in the experimental cohort of 48 animals.