Meeting Abstract

5.2  Sunday, Jan. 4  Comparing two life history strategies in a changing environment MARTIN, Shannon B.*; LEBERG, Paul L.; University of Louisiana at Lafayette; University of Louisiana at Lafayette sbm@louisiana.edu

As the Earth’s climate changes and sea level rises, more saline waters will encroach into traditionally freshwater coastal habitats with greater frequency. These environmental changes stress resident organisms affecting their reproductive fitness. To evaluate the effects of increasing salinity on reproductive allocation, Gambusia affinis and Heterandria formosa were collected from populations along a salinity gradient and maintained in a common freshwater environment for six generations. We performed an experiment on pregnant F6 females using a factorial design of historical and contemporary salinity treatments to examine the influence of salinity on offspring size and number in these two livebearing fish species that have different strategies of offspring provisioning. In the primarily lecithotrophic G. affinis, we found that the historical salinity influenced the number of offspring while the contemporary gestational salinity impacted offspring size. In support of the Trexler-DeAngelis model, we detected plasticity in post-zygotic offspring provisioning under an ad libitum feeding regime. Our results suggest that G. affinis from fresh and intermediate marshes were facultatively matrotrophic by increasing offspring size after fertilization while females from brackish marshes were lecithotrophic. Contrasting results were obtained for the highly matrotrophic H. formosa. Both species, however, exhibited genetic variation in phenotypic plasticity and utilized maternal effects to vary the number and size of their offspring in an attempt to maximize their fitness (i.e., fecundity and offspring quality) in environments with different salinity levels.