Applying geometric morphometrics in megalopa larval stages: relevance for species distribution and biological invasion studies

Larval morphology in brachyuran crabs is an essential trait defining survival in the planktonic environment. The present study describes the morphology (carapace and chelipeds) of megalopa larvae in three different species (Percnon gibbesi, Cronius ruber, and Achelous hastatus) using geometric morphometric analysis (gma). The study aim was to compare the observed body patterns at interspecific and intraspecific levels. The results showed a marked interspecific distinction of C. ruber larvae based on the rostral region of carapace and cheliped length. We relate these differences to advantages in life performance, as in other animal models, suggesting that larval morphology can be another factor contributing to the invasiveness of C. ruber. At intraspecific level, we found a high morphological similarity between two distant geographical locations, indicating strong genetic connectivity in the populations of P. gibbesi from the Canary Islands. Our findings advance the importance of larval morphology for species performance during the plankton phase that eventually can determine invasiveness in brachyuran crabs. We suggest future studies focusing on the inter-population comparisons of megalopa morphology at larger spatiotemporal scales.