DESCRIPTION OF THE MALE LEPIDURUS ARCTICUS (BRANCHIOPODA: NOTOSTRACA) AND THE POTENTIAL ROLE OF CANNIBALISM IN DEFINING MALE FORM AND POPULATION SEX RATIO.

Sexual dimorphism in the Arctic tadpole shrimp, Lepidurus arcticus (Pallas, 1793), was examined. Selective forces shape sexes differently. Males fitness increases by successful mate searching, whereas females increase reproductive potential by attaining large sizes. Sexual dimorphism was examined in 331 L. arcticus from Svalbard, Norway. Males were significantly smaller than females and had significantly smaller carapaces, telsons and cercopods. Lepidurus arcticus is an omnivorous, sometimes cannibalistic, predator. Cannibalism potential effects on sexual dimorphism were studied in the field and laboratory. Cannibalism frequency did not differ significantly between populations. Females dominated in all populations. Male L. arcticus searching for females are at greater risk due to increased chance of encounters with predators and cannibalistic females. Male small body size is advantageous against visually hunting predators, while more robust limbs help males search for females effectively and amplex them. In contrast, the significantly larger female carapace protects her and her eggs from predators. [ABSTRACT FROM AUTHOR]