The implications of temperature-mediated plasticity in larval instar number for development within a marine invertebrate, the shrimp Palaemonetes varians

Variations in larval instar number are common among arthropods. Here, we assess the implications of temperature-mediated variations in larval instar number for larval development time, larval growth rates, and juvenile dry weight within the palaemonid shrimp, Palaemonetes varians. In contrast with previous literature, which focuses on terrestrial arthropods, particularly model and pest species often of laboratory lines, we use wild shrimp, which differ in their life history from previous models. Newly-hatched P. varians larvae were first reared at 5, 10, 17, 25, and 30°C to assess their thermal scope for development. Larvae developed at 17, 25, and 30°C. At higher temperatures, larvae developed through fewer larval instars. Two dominant developmental pathways were observed; a short pathway of four instars and a long pathway of five instars. Longer developmental pathways of six to seven instars were rarely observed (mostly at lower temperatures) and consisted of additional instars as ‘repeat’ instars; i.e. little developmental advance over the preceding instar. To assess the implications of temperature-mediated variation in larval instar number, newly-hatched larvae were then reared at 15, 20, and 25°C. Again, the proportion of larvae developing through four instars increased with temperature. At all temperatures, larval development time and juvenile dry weight were greater for larvae developing through five instars. Importantly, because of the increasing proportion of larvae developing through four instars with increasing temperature, larval traits associated with this pathway (reduced development time and juvenile dry weight) became more dominant. As a consequence of increasing growth rate with temperature, and the shift in the proportion of larvae developing through four instars, juvenile dry weight was greatest at intermediate temperatures (20°C). We conclude that at settlement P. varians juveniles do not follow the temperature-size rule; this is of importance for life-history ecology in response to environmental change, as well as for aquaculture applications

Desenvolvimento "in vitro" de larvas e juvenis de Emerita brasiliensis Schmitt (Crustacea, Decapoda, Hippidae) sob diferentes condições de temperatura, salinidade e regime alimentar "In vitro" development of larvae and juveniles of the sand crab Emerita brasiliensis Schmitt (Crustacea, Decapoda, Hippidae) under different conditions of temperature, salinity and food diet

Larvas eclodidas em laboratório e juvenis coletados em campo do tatuí Emeritabrasiliensis (Hippidae) foram cultivados em diferentes temperaturas e regime alimentar com a finalidade de avaliar as melhores condições para a manutenção da espécie em laboratório. O efeito da freqüência da substituição da água de cultivo sobre o desenvolvimento larvar também foi estudado avaliando-se a sobrevivência, o crescimento e a duração dos estádios larvares. A duração das fases larvares e o crescimento das três últimas fases de zoea correlacionaramse positivamente com a temperatura. As temperaturas testadas, entre 18 e 26ºC não influenciaram a sobrevivência das larvas. Não houve influencia da alimentação e nem da troca de água no desenvolvimento, crescimento e sobrevivência das larvas, bem como das dietas de microalgas na sobrevivência e desenvolvimento dos juvenis.<br>Hatched larvae and field sampled juveniles of the sand crab Emeritabrasiliensis were reared at different temperatures and food diet in order to evaluate the best conditions for laboratory maintenance. The effects of frequency of changing the aquarium seawater on larval development was also studied evaluating the survival, growth and duration of larval stages. The duration of larval stage and growth of the last three zoes phases correlate positively with temperature. Temperatures between 18 and 26ºC did not influence the larval survival. The kind of food and frequency of water exchange did not influence the development, growth, and survival of larvae, as well as the development, and survival of juveniles