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The sex lives of ctenophores: the influence of light, body size, and self-fertilization on the reproductive output of the sea walnut, Mnemiopsis leidyi - PubMed

  • ️Fri Jan 01 2016

The sex lives of ctenophores: the influence of light, body size, and self-fertilization on the reproductive output of the sea walnut, Mnemiopsis leidyi

Daniel A Sasson et al. PeerJ. 2016.

Abstract

Ctenophores (comb jellies) are emerging as important animals for investigating fundamental questions across numerous branches of biology (e.g., evodevo, neuroscience and biogeography). A few ctenophore species including, most notably, Mnemiopsis leidyi, are considered as invasive species, adding to the significance of studying ctenophore ecology. Despite the growing interest in ctenophore biology, relatively little is known about their reproduction. Like most ctenophores, M. leidyi is a simultaneous hermaphrodite capable of self-fertilization. In this study, we assess the influence of light on spawning, the effect of body size on spawning likelihood and reproductive output, and the cost of self-fertilization on egg viability in M. leidyi. Our results suggest that M. leidyi spawning is more strongly influenced by circadian rhythms than specific light cues and that body size significantly impacts spawning and reproductive output. Mnemiopsis leidyi adults that spawned alone produced a lower percentage of viable embryos versus those that spawned in pairs, suggesting that self-fertilization may be costly in this species. These results provide insight into the reproductive ecology of M. leidyi and provide a fundamental resource for researchers working with them in the laboratory.

Keywords: Body size; Ctenophore; Cues; Hermaphrodite; Inbreeding depression; Mnemiopsis leidyi; Reproduction; Sea walnut; Self-fertilization; Spawn.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1. Diagram used to estimate egg numbers in M. leidyi.

Each triangle (labeled 1–8) represents 7.96% of the total area of the circle. We counted the eggs in two triangles and then multiplied the total by 6.285 to estimate the total number of eggs in the dish. Scaled to actual size used for round glass bowls 2″ in diameter.

Figure 2
Figure 2. Cubic spline showing the effect of body size of M. leidyi on the likelihood to spawn.

Points along the lower x-axis indicate individuals that did not spawn, while points on the upper x-axis indicate individuals that did spawn. Multiple individuals of the same size may be represented by a single point. Ctenophores smaller than 26 mm (section A) rarely spawned (1/22 = 5%) while those larger than 30 mm (section C) almost always spawned (77/80 = 96%). Nearly half of the individuals between 26 and 30 mm spawned (section B, 6/16 = 38%). Lambda value of cubic spline set to 1.

Figure 3
Figure 3. Effect of body size on egg production in M. leidyi.

Larger individuals generally produced more eggs than smaller individuals (N = 30, r2 = .38, p < 0.001). Only those animals that spawned 25 or more eggs are included in the analysis and figure.

Figure 4
Figure 4. Correlation between body size and egg viability in M. leidyi.

Body size positively correlated with the percentage of eggs that developed after 24 h, although the result was not significant (N = 29, r2 = 0.12, p = 0.07).

Figure 5
Figure 5. Estimated number of eggs in bowls of individuals that spawned alone (N = 30 bowls) and in pairs (N = 25 bowls).

Surprisingly, two M. leidyi spawning together did not produce more eggs than individuals spawning alone (Student’s t-test, t-ratio = 0.005, p = 1.0). The data point above the “Alone” box plot indicates an individual that spawned an estimated 3,934 eggs. Removing this data point did not change the overall findings of the analysis.

Figure 6
Figure 6. Percentage of eggs developed after 24 h for individuals M. leidyi spawning alone (N = 29 bowls) and in pairs (N = 25 bowls).

A higher percentage of eggs developed for M. leidyi in pairs, possibly suggesting a cost to self-fertilization (Student’s t-test, t-ratio = 2.3, df = 52, p = 0.025). Asterisk indicates significant difference across treatments.

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Grants and funding

This work was funded with startup funds to Joseph Ryan from the University of Florida DSP Research Strategic Initiatives and the Office of the Provost. This material is based upon work supported by the National Science Foundation under Grant No. (1542597). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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