Competing influences on morphological modularity in biomechanical systems: a case study in mantis shrimp

Area of Science:

• Evolutionary Biology
• Comparative Morphology
• Biomechanics

Background:

• Morphological covariation, the correlated variation of traits, is crucial for understanding evolutionary constraints and developmental integration.
• Mantis shrimp (Stomatopoda) possess complex raptorial appendages used for predation, exhibiting diverse feeding strategies (spearing vs. smashing).
• Understanding covariation patterns in these appendages can illuminate how different selective pressures shape morphology.

Purpose of the Study:

• To investigate and compare patterns of morphological covariation in the raptorial appendages of a mantis shrimp spearer (Squilla empusa) and a smasher (Gonodactylaceus falcatus).
• To assess the influence of biomechanical frameworks and segmentation-based developmental pathways on covariation.
• To explore how factors like sex and population structure affect covariation patterns.

Main Methods:

• Collected morphometric data from Squilla empusa specimens.
• Analyzed previously published morphometric data for Gonodactylaceus falcatus.
• Compared covariation patterns using three modularity frameworks (two biomechanical, one segmentation-based).

Main Results:

• Significant differences in morphological covariation were observed between the spearer and smasher mantis shrimp species.
• Covariation patterns varied depending on whether data were analyzed collectively or subdivided by sex or sub-population.
• An unusual handedness pattern was identified: right appendages showed variable spine numbers, while left appendages had constant numbers.

Conclusions:

• The study underscores the necessity of evaluating multiple theoretical frameworks when examining morphological covariation.
• Feeding mechanisms (spearing vs. smashing) exert contrasting influences on covariation in mantis shrimp appendages.
• Findings highlight the complex interplay between development, biomechanics, and ecology in shaping evolutionary trajectories.