Size-Assortative Pairing in the Big-Clawed Snapping Shrimp, Alpheus Heterochelis

Abstract

The big-clawed snapping shrimp, Alpheus heterochelis, is found in size-matched male-female pairs. A common assumption is that a large size advantage in males, an extended pair bond, and a positive correlation between female size and fecundity promotes size-assortative pairing. Since all of these conditions apply to A. heterochelis, we investigated size-assortative pairing in the laboratory by designing experiments in which the pairs were size matched or mismatched using three size categories; large, medium and small. We found that snapping shrimps prefer to pair according to size and that such pairing is stable. We also found that, contrary to the initial assumptions, female-female competition and female choice for large males plays the main role in the pair formation process. Smaller, and hence less competitively successful, females will pair with smaller males, but in a male-biased environment, will preferentially pair with larger males. Large males provide the best protection from shelter eviction, which is crucial for female A. heterochelis, as their reproduction is closely associated with moult, and therefore requires shelter and a male present for successful reproduction.

Parental Roles and the Amount of Care In a Bi-Parental Substrate Brooding Cichlid: The Effect of Size Differences Within Pairs

“…Size-dependent mate choice by either or both sexes and associated intrasexual competition may be the major force producing size-assortative mating (e.g. McKaye, 1986;Crespi, 1989;Rahman et al, 2002). This may be the case for J. ornatus, showing high fecundity of large females and predominance in intrasexual competition of large individuals of both sexes (Awata, unpubl.…”

Social Behaviour and Recognition in Decapod Shrimps, with Emphasis on the Caridea

“…In the big-clawed snapping shrimp Alpheus heterochaelis, which typically live in size-matched mating pairs, females would approach larger or same-sized males more often than smaller males and show more aggression (snapping) towards mates that are not size-matched (Rahman et al 2002. This indicates that females recognize the sizes of a potential mate; such recognition is not observed in males.…”

Why have long antennae? Exploring the function of antennal contact in snapping shrimp

“…Body size also plays a role in pairing interactions; in field-captured pairs of both species, body sizes are correlated (Nolan and Salmon 1970;Schein 1975;Hughes 1996a;Mathews 2002b). Although male snapping shrimp may benefit from mating with larger females, given that female body length is highly correlated with clutch size (Knowlton 1980), A. heterochaelis males show no preference for larger females (Rahman et al 2002. In contrast, females actively seek out larger males, and larger females are more likely than smaller females to approach larger males .…”

“…Females may prefer larger males because larger males are better competitors, thus potentially providing better protection and/or defense of their shared burrow (Hughes 1996b;Rahman et al 2004). Size-assortative pairing may thus be the result of females pairing with the largest male they can successfully compete for and defend from other females (Rahman et al 2002). If tactile information regarding body size is assessed via direct antennal contact, then A. heterochaelis females would be predicted to engage in more antennal contact during pairing than males.…”

“…Given the potential high risk of injury in competitive interactions, we predicted that antennal contact would be greater in pairing interactions than in competitive interactions or interactions with heterospecifics. As Rahman et al (2002Rahman et al ( , 2004 found that female A. heterochaelis actively seek out larger individuals for pairing, whereas male A. heterochaelis showed Marine and Freshwater Behaviour and Physiology 163 no preference for females based on either size or molt status (Rahman et al 2003), we hypothesized that females play a more active role in pair formation in A. heterochaelis, and therefore predicted that when pairing, female A. heterochaelis would perform more antennal contact than males. In contrast, as Mathews (2003) found that male A. angulosus actively seek out pre-molt females, we hypothesized that males play a more active role in pair formation in A. angulosus, and predicted that when pairing, male A. angulosus would perform more antennal contact than females.…”