Detecting sex‐related differences in mesograzer feeding experiments: An often overlooked source of intraspecific variation in herbivory

Abstract

Nutritional demands of males vs. females can be markedly different, leading to potential differences in food utilization within natural populations. However, widely‐used experimental approaches to determine food choice and feeding rates of marine consumers seldom detect sex‐related differences in feeding. Such studies have expressed consumption results largely per experimental replicate or per individual. By using small modifications of these methods, and alternative ways of expressing consumption, we tested for sex‐related differences in feeding in the amphipod Gammarus aequicauda and the crab Omalacantha bicornuta. Males and females of the amphipod showed similar preferences for Ulva cf. prolifera over Cladophora glomerata in pairwise choice assays. In contrast, females of the crab significantly preferred the alga Acanthophora spicifera over Ulva fasciata, but males expressed no preference. While choice was not affected by different ways of expressing feeding, we showed that standardizing results by consumer mass highlighted significant differences in total consumption and feeding rates in both choice and no‐choice conditions. For both mesograzers, females consumed significantly more algae per mass than males when total consumption from the choice experiments was analyzed. Similarly, when confined to single diets (no‐choice), feeding rates of females standardized by female mass were significantly higher for both consumers. Expressing consumption as algal mass eaten by individual, individual length, or individual width, failed to detect any sex‐related differences for these two consumers. Using consumer mass in analyzing feeding experiments can help elucidate poorly understood patterns of intraspecific variation in marine grazers.

The behavior of Gammarus aequicauda (crustacea, amphipoda) during predation on chironomid larvae: Sex differences and changes in precopulatory mate‐guarding state

“…Females consume plant food somewhat more intensively than males, which also have been shown for G. aequicauda in other experiments (Cruz-Rivera et al, 2017). Experiments have shown that males in the presence of chironomid larvae do not consume Ruppia leaves, which begin to be consumed only sometime after the larvae have been completely eaten.…”

“…Diet formation is influenced by various abiotic and biotic factors, including intrapopulation ones (Hargrave & Geen, 1970;Ivlev, 1961;Shadrin et al, 2020a;Varley et al, 1974), the relationship of which remains poorly understood for most animal taxa. As an example, currently, there are numerous studies of sex-driven variation in the feeding of different terrestrial animals, from insects to mammals, but only a few studies on sexual differences in marine invertebrates (Cruz-Rivera et al, 2017). Amphipods often play a key role in the functioning and dynamics of various aquatic ecosystems occupying different trophic niches (Evagelopoulos et al, 2008;Kinne, 1959;Kelly et al, 2002;Mancinelli, 2012;Shadrin et al, 2019Shadrin et al, , 2020a.…”

“…Animals determine behaviors regarding their physiological needs and reproductive goals (Cozzoli et al, 2018(Cozzoli et al, , 2020Prato et al, 2006;Shokri et al, 2019Shokri et al, , 2021Shuhaimi & Pascoe, 2001), once they reach sexual maturity, new dimensions would be added to their internal state and hence, the organism foraging decisions (Becker et al, 2012;Cruz-Rivera et al, 2017;Mowrey & Portman, 2012;Ward, 1985Ward, , 1986. Sex-related differences were shown in G. aequicauda during its feeding as a grazer on two green algae species (Cruz-Rivera et al, 2017). Amphipod females as well as some other crustacean taxa, mature earlier than males and are capable of being fertilized within a very short time immediately after molting (Jormalainen, 1998;Kuribayashi et al, 2006;Pinheiro & Fransozo, 1999).…”