First report of Gonodactylus smithii (Pocock, 1893) from South Andaman, India (Crustacea : Stomatopoda)

The Andaman and Nicobar group of islands (11.7401°N, 92.6586°E) are surrounded by the Bay of Bengal to the west and Andaman Sea to the east. The species reported in this paper belongs to the superfamily Gonodactyloidea, which are generally “smashers”, i.e. the dactylus of their raptorial appendage is greatly inflated at the base and used to break open hard-bodied prey (Ahyong 1997). Most smashers live in rock and coral cavities and have a heavily armoured telson for defensive and offensive purposes (Caldwell & Dingle 1975). Studies on the family Gonodactylidae from these islands have been limited and few have been reported so far (Jayabarathi et al. 2013; Kumaralingam & Raghunathan 2016; Kumaralingam et al. 2017). Recent field studies in the Andaman Islands collected a specimen of the Gonodactylus smithii, reported herein.

Mechanical sensitivity and the dynamics of evolutionary rate shifts in biomechanical systems

The influence of biophysical relationships on rates of morphological evolution is a cornerstone of evolutionary theory. Mechanical sensitivity—the correlation strength between mechanical output and the system's underlying morphological components—is thought to impact the evolutionary dynamics of form–function relationships, yet has rarely been examined. Here, we compare the evolutionary rates of the mechanical components of the four-bar linkage system in the raptorial appendage of mantis shrimp (Order Stomatopoda). This system's mechanical output (kinematic transmission (KT)) is highly sensitive to variation in its output link, and less sensitive to its input and coupler links. We found that differential mechanical sensitivity is associated with variation in evolutionary rate: KT and the output link exhibit faster rates of evolution than the input and coupler links to which KT is less sensitive. Furthermore, for KT and, to a lesser extent, the output link, rates of evolution were faster in ‘spearing’ stomatopods than ‘smashers’, indicating that mechanical sensitivity may influence trait-dependent diversification. Our results suggest that mechanical sensitivity can impact morphological evolution and guide the process of phenotypic diversification. The connection between mechanical sensitivity and evolutionary rates provides a window into the interaction between physical rules and the evolutionary dynamics of morphological diversification.

Intraspecific agonistic interactions of squilla empusa (crustacea: stomatopoda)

Mantis shrimp are benthic, predatory marine crustaceans that have complex agonistic interactions. These crustaceans are divided into two functional groups based on the morphology and use of their raptorial appendage: smashers and spearers. Most research on the agonistic behaviours of mantis shrimp has focused on smasher species and on contests between asymmetrical and same-sex individuals. No studies have investigated the intersexual and intrasexual interactions of size-matched spearer individuals. I conducted a laboratory experiment using Squilla empusa, a spearer that lives in the Gulf of Mexico, to determine if agonistic differences exist between males and females. The results suggest that (1) although threat displays are rare in both males and females, male aggressive interactions involving physical contact are common, (2) males engage in more aggressive behaviours and interactions than do females, (3) females are less aggressive toward both males and females than males are toward males and females; interactions involving females are usually passive, non-striking, whereas interactions involving males can result equally in a strike or passive behaviour, (4) males are more aggressive than females, and (5) an increase in the number of treatment individuals resulted in an increase in the number of interactions. The behaviours of Squilla empusa are compared with literature reports concerning other species of mantis shrimp. The differences in habitat, feeding method, vision, and burrow type may explain the differences between smashers and spearer agonistic behaviours.