Costs of delayed metamorphosis: reduced growth and survival in early juveniles of an estuarine grapsid crab, Chasmagnathus granulata

Abstract

When the megalopa stage of estuarine crab species becomes competent for settlement and metamorphosis, it responds to specific chemical and physical cues from the adult environment. Delayed metamorphosis in the absence of such cues is beneficial insofar as it increases the probability of finding a suitable habitat, and it may also enhance the genetic exchange between separate populations. However, this developmental and behavioural response may incur energetic costs reducing the fitness of later life-history stages. In a laboratory investigation, we studied postmetamorphic consequences of delayed metamorphosis for growth and survival in early juvenile instars (I through V) of an estuarine grapsid crab, Chasmagnathus granulata (Dana, 1851). In competent megalopa larvae of this species, metamorphosis is induced by chemical cues from muddy substrates and conspecific adults (control treatment). After delayed metamorphosis in the absence of these cues (experimental treatment), survival and body size were significantly reduced in the first crab stage, and the duration of development to the second juvenile instar was significantly longer. Survival, moult-cycle duration, and percentage growth increments were not significantly affected in later juvenile instars. However, as a consequence of the initial reduction in development and growth, the crabs from the experimental treatment remained consistently smaller and moulted later to successive instars than in the control group. Our results indicate that delayed metamorphosis is associated with a reduced postmetamorphic fitness in an estuarine crab species.