Sexual selection on the seashore: Mating systems of marine arthropods

Dr. Vik Iyengar
Biology Department, Villanova University

Arthropods are the most abundant and diverse group in the animal kingdom – they occupy nearly every ecological niche in marine, freshwater and terrestrial habitats.  Their extraordinary evolutionary success can be partly attributed to the remarkable diversity of mating systems found in arthropods.  I am primarily interested in sexual selection, particularly within species that are sexually dimorphic – that is, where strong competition for mates has ultimately lead to divergence in the appearance of males and females.  Exaggerated male traits can be the result of female choice, where females mate preferentially based on the male’s expression of these traits, male competition, where males use armaments in intrasexual battles for access to females, or a combination of both.  In such mating systems, males usually compete with each other for females in contests usually determined by differences in body size or weaponry which dictate fighting ability. Males may compete directly for access to females or may instead control resources essential for female survival and reproduction.







Earwigs are a model system for studying competition and reproductive behavior because they are distinguished by their possession of weapons (“forceps”), their high degree of maternal care (females aggressively guarding eggs and juveniles), and high densities that promote frequent interaction.

In most earwigs, both sexes use their forceps to capture prey, and female earwigs are usually larger than males, presumably due to a fecundity advantage seen in many arthropods.  The maritime earwig Anisolabis maritima is unusual among the order Dermaptera, and this insect is particularly well-suited for studies of sexual selection because males differ markedly from females in both body size (males are more variable in size, and often substantially larger, than females) and weaponry (males possess asymmetrical, curved forceps whereas females have straight forceps; see photo). Furthermore, while females often kill conspecifics by using their forceps like scissors, males usually resolve their disputes non-lethally by squeezing each other’s abdomens, perhaps a means to assess strength and fighting ability (see diagram from Muñoz & Zink 2012).

Muñoz & Zink 2012










This summer we will continue lab and field investigations of the mating system of A. maritima by determining the roles of sex, size and weaponry on intrasexual competition and intersexual mating preferences, and by examining how same-sex and mixed-sex interactions (“social networks”) affect distribution patterns observed in the field.

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