Morphometric correlations between dietary and reproductive traits of two brachyuran crabs, Hemigrapsus sanguineus and Aratus pisonii

Many animals have flexible morphological traits that allow them to succeed
in differing circumstances with differing diets available to them. For
brachyuran crabs, claw height and gut size are diet-specific and largely
reflect foraging strategies, while abdomen width reflects relative levels
of fecundity. However, the link between claw size and diet has largely
been documented only for primarily carnivorous crabs, while the link
between diet and fecundity is strong in herbivorous crabs. We sought to
determine the nature of the intraspecific relationship between claw size,
dietary habits, and fecundity for two primarily herbivorous crab species,
Hemigrapsus sanguineus and Aratus pisonii. Specifically, we examined
whether claw size and/or abdomen width can be used as reliable measures of
individual diet strategy. To test these hypotheses, we collected crabs and
measured the dimensions of their claws, abdomens, and guts. By comparing
these dimensions for each individual, we found that strongly predictive
relationships do not exist between these traits for the primarily
herbivorous species in our study. Thus, identifying external morphological
features that can be used to assess diets of primarily herbivorous crabs
remains elusive.