Allometry and sexual dimorphism of the sensory flagella in three species of crayfishes (Decapoda: Astacidea: Cambaridae)

Abstract Sensory flagella are central to the ecology and behavior of decapod crustaceans, mediating navigation, foraging, and reproduction through detection and manipulation of environmental and conspecific-relevant information. Crayfishes possess five pairs of flagellated structures: one pair of uniramous antennae, one pair of biramous antennules, and three pairs of uniramous fan organs, but comparative studies of these structures are rare, particularly for antennules and fan organs. We conducted a comparative analysis of flagellar morphology across three ecologically distinct crayfishes: Faxonius obscurus (Hagen, 1870), Cambarus carinirostris (Hay, 1914), and C. monongalensis Ortmann, 1905. We tested for interspecific variation, sexual dimorphism, and conserved morphological phenotypes across flagella using linear measurements and allometric analyses. We found significant interspecific differences in both length and somite number, with F. obscurus exhibiting the longest antennae and antennules with the most somites, consistent with adaptation to flowing-water environments, whereas C. monongalensis possessed shorter structures with many somites in fan organs, likely reflecting specialization for inhabiting burrows. Sexual dimorphism was detected primarily in antennules, where males and females differed in intercepts and slopes of allometric relationships, while fan organs showed little evidence of sex-specific variation. Flagella consistently exhibited conserved tapering from stout basal to slender distal somites across species, likely reflecting a biomechanical constraint. These findings demonstrate that crayfish flagella evolve under the joint pressures of ecology, biomechanics, and sexual selection, highlighting their value as a model system for investigating the evolution of sensory morphology in decapods.