PARENT SESSION
Contributed Oral Session 61: Evolutionary Ecology: Aquatic Systems
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 518 A, Level 5, Palais des congrès de Montréal

On the evolution of protandric-simultaneous hermaphroditism in the shrimp Lysmata wurdemanni: A consequence of sex-dependent energetic costs, mortality rates, or time commitments?

Baeza, J. Antonio^*,1, ¹ Department of Biology, The University of Louisiana at Lafayette, Lafayette, LA, USA

ABSTRACT- Protandric simultaneous hermaphroditism (PSH), as recently reported for shrimps in the genus Lysmata, is a novel sexual system in which individuals invariably reproduce as males first (MP individuals) and later in life as simultaneous hermaphrodites (SHP individuals). I test here three recently proposed models (i.e., sex-dependent energetic costs, time commitments, and mortality rates) explaining the evolution of PSH in the shrimp L.wurdemanni. Specific predictions/assumptions of each model were evaluated in the laboratory using observational/manipulative experiments. I found no evidence that the sex-dependent mortality model explains PSH in the studied species because mortality suffered by SHPs due to predatory fishes was not greater but similar to that suffered by MPs, in contrast to that predicted by this model. On the other hand, MPs grew faster than SHPs in the laboratory suggesting that the female function incurs higher energetic costs of reproduction than the male function. SHPs were also more successful in monopolizing food than smaller MPs in a competitive environment. This sex-dependent growth rate and size-dependent resource holding power agree with predictions of the sex-dependent energetic cost model explaining the evolution of PSH in L.wurdemanni. At last, the time SHPs required to replenish their sperm reservoir after mating as males was shorter than the time they required to produce and brood two consecutive eggs clutches. Small SHPs also experienced a heavier mortality rate by fish predators than large SHPs. This sex-dependent reproductive time commitment and size-dependent mortality agree with predictions of the sex-dependent time commitment model that additionally explain the evolution of PSH in L.wurdemanni. This study stresses the necessity of explaining the evolution of strict simultaneous and sequential hermaphroditism, as well as mixed sexual systems such as PSH with a single comprehensive theoretical model.

Key words: sex allocation, sexual system, hermaphrodite, shrimp