Temperature modulates compensatory responses to food limitation at metamorphosis in a marine invertebrate

Abstract

Under climate change, increased temperatures combined with food limitation may be critical for species with complex life cycles, if high growth rates characterize the larval development. We studied the effect of increased temperature and food limitation on larval survival and on functional traits (developmental time, body mass, growth) at moulting and metamorphosis in the crab Carcinus maenas. We followed the approach of models of metamorphosis integrating responses of body mass and developmental time to increased temperature and food limitation. We also evaluated if body mass decreased with temperature (according to the temperature-size rule) and if developmental time followed an inverse exponential reduction (expected from some metabolic theories), as both trends are relevant for modelling effects of climate change on fitness and population connectivity. Larvae produced by four females were reared separately from hatching to metamorphosis to the megalopa at two food conditions (ad libitum and food limitation), and at four temperatures covering the range experienced in the field (<20°C) and those expected from climate change (>20°C). In general, body mass did not decrease with temperature, nor developmental time followed an inverse exponential response to temperature (under ad libitum food conditions). At low temperatures (<20°C), food limitation resulted (in general) in small reductions in larval survival. Body mass and nitrogen content were little affected by food limitation while effects on carbon content were small. Increased developmental time partially or fully compensated for reduced growth rates. We interpreted this response as adaptive, as minimizing fitness costs associated to reduced body mass. Increased temperatures (>20°C) exacerbated the effect of food limitation on mortality in larvae from three females. Developmental time was longer and larvae metamorphosed with reduced body mass, carbon and nitrogen content. Thus, compensatory responses failed and multiple fitness costs should be expected in individuals facing food limitation at increased temperatures. We propose that integrative studies of traits at metamorphosis could be a basis to develop a mechanistic understanding of how species with complex life cycles will respond to climate change. Such models could eventually include hormonal and metabolic regulation of development as drivers of responses to environmental change.