Title

Sperm storage and sexual selection in Aplysia californica, a simultaneous hermaphrodite

Date of Award

2006

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Marine Biology and Fisheries

First Committee Member

Patrick J. Walsh, Committee Chair

Abstract

The California sea hare, Aplysia californica, is a simultaneous hermaphrodite opisthobranch mollusk. This organism is bred and reared in captivity at the National Institutes of Health (NIH), National Center for Research Resources (NCRR), National Resource for Aplysia at the University of Miami. A. californica readily mate in the laboratory and perform unilateral copulations with the sperm donor on top of the sperm recipient. A. californica also possess a complex reproductive system that includes a seminal receptacle for the storage of sperm received from mating (allosperm). Based on their behavior and reproductive reproductive anatomy, A. californica should provide a model for the study of simultaneous hermaphrodite mating systems. Using controlled matings, scnDNA - RFLP genetic markers and careful observation of mating behavior and the development of embryos over time, we analyze A. californica 's ability to store and use exogenous sperm in relation to their mating behavior. On average, A. californica (240.6 +/- 31.7 gram; mean +/- SE, N = 9) produced 8.8 +/- 0.6 egg masses containing a total of 16.9 +/- 2.2 X 106 fertilized eggs over a period of 22.3 +/- 3.6 days following a single mating. The primary factors determining the cumulative number of viable eggs produced from a single mating in A. californica were the mass of the sperm recipient (r = 0.773, p < 0.05, n = 9) and the mass of the sperm donor (r = 0.625, p < 0.10, n = 9). Our results demonstrated that A. californica are not sperm limited following a single mating. A. californica who acted as sperm recipient in their initial mating encounter showed a highly significant preference for acting as the sperm donor in subsequent matings, when paired with a "virgin" partner (Chi2 = 10.714, p = 0.0011, df = 1, n = 21) (Figure 3.1). However, this preference disappeared after the initial sperm recipient spawned a fertilized egg mass prior to their second mating bout (Chi2 = 1.24, p = 0.265, df = 1, n = 13) (Figure 3.5). As a consequence, I was able to verify second donor sperm precedence in a single clutch from a multiple sperm recipient. These results support the hypothesis that depletion of stored allosperm plays a crucial role in the resolution of sexual conflict and the mating decisions of A. californica . These results reveal a level of flexibility in the mating decisions of simultaneous hermaphrodites not predicted by current models of behavior for the sustainability of hermaphroditism. Future work should focus on adjustments in mating behavior in response to changing environmental conditions as well as further verification of sperm precedence in this species.

Keywords

Biology, Oceanography; Biology, Zoology

Link to Full Text

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