Hormonal dynamics of matrotrophy vs. lecithotrophy in live-bearing fish reproduction.

We explored the relationship between gestational states, fecundity, and steroid hormone levels in three species of live-bearing fish with different maternal provisioning strategies. We studied two lecithotrophic species, Gambusia affinis and Xiphophorus couchianus, where embryos feed exclusively on yolk stored in the eggs, and one matrotrophic species, Heterandria formosa, which actively transfers nutrients to embryos through a follicular placenta. We measured water-borne cortisol, estradiol, and progesterone along with brood size (fecundity) and gestational stage(s).

River zebrafish combine behavioral plasticity and generalized morphology with specialized sensory and metabolic physiology to survive in a challenging environment.

Phenotypes that allow animals to detect, weather, and predict changes efficiently are essential for survival in fluctuating environments. Some phenotypes may remain specialized to suit an environment perfectly, while others become more plastic or generalized, shifting flexibly to match current context or adopting a form that can utilize a wide range of contexts. Here, we tested the differences in behavior, morphology, sensory and metabolic physiology between wild zebrafish (Danio rerio) in highly variable fast-flowing rivers and still-water sites.

Resource availability and its effects on mother to embryo nutrient transfer in two viviparous fish species.

Different hypotheses have been proposed to explain the adaptive value of matrotrophy, which is the postfertilization maternal provisioning to developing embryos. The Trexler-DeAngelis model proposes that matrotrophy provides fitness advantages when food abundance is high and availability is constant. If food availability is low or unpredictable, prefertilization maternal provisioning (lecithotrophy) should be favored over matrotrophy.

Losing the trait without losing the signal: Evolutionary shifts in communicative colour signalling.

Colour signalling traits are often lost over evolutionary time, perhaps because they increase vulnerability to visual predators or lose relevance in terms of sexual selection. Here, we used spectrometric and phylogenetic comparative analyses to ask whether four independent losses of a sexually selected blue patch are spectrally similar, and whether these losses equate to a decrease in conspicuousness or to loss of a signal. We found that patches were lost in two distinct ways: either increasing reflectance primarily at very long or at very short wavelengths, and that species with additional colour elements (UV, green and pink) may be evolutionary intermediates.