The morphology–diet relationship and its role in the coexistence of two species of annual fishes

Abstract

Annual fishes, which inhabit temporary pools with extremely limited habitat complexity and niche availability, display remarkable sexual dimorphism, rapid growth, and enormous investment into reproduction, all traits associated with high energy requirement. This study tests three hypotheses for two syntopic annual fishes (Austrolebias minuano and Cynopoecilus fulgens) found in six wetlands of southern Brazil: (i) considerable morphological differences result in low dietary overlap, (ii) sexual dimorphism in both species leads to intraspecific diet segregation, and (iii) dietary richness increases during ontogenetic development, and is narrower in C. fulgens than A. minuano due to morphological limitations imposed by reduced size. The diet of 82 A. minuano and 211 C. fulgens individuals was analyzed over two annual cycles. The morphology was characterized by 26 measurements covering the entire body of both species. There was no evidence of morphological specialization related to food competition and the diet of A. minuano and C. fulgens showed high overlap. High food availability, high predator abundance, and high connectivity of adjacent wetlands are likely the main mechanisms allowing coexistence of both species. Within species, sexual dimorphism did not result in a decrease in dietary overlap, which reinforces the idea that morphological differences between the sexes did not evolve as a mechanism to decrease food competition. Large A. minuano did not have a more diverse diet than the smaller C. fulgens; however, increase in body size allowed both species to ingest larger prey. Morphological variability in both species was mainly related to ontogenetic development and reproduction.

Ontogenetic variations and feeding habits of a Neotropical annual fish from southern Brazil

“…Ontogenetic feeding changes are well known in fishes (Wootton, 1999;Amundsen et al, 2003) and have been recorded in some Cynolebiidae species (Santos-Filho, 1997;Laufer et al, 2009;Abilhoa et al, 2010b;Canavero et al, 2013;Keppeler et al, 2013Keppeler et al, , 2015Cavalheiro & Fialho, 2016;Ortiz & Arim, 2016). These ontogenetic changes in annual fish populations may reduce a potential intraspecific competition for prey items through diet segregation or by reducing direct interactions through spatial and/or temporal segregation (Laufer et al, 2009;Canavero et al, 2013;Ortiz & Arim, 2016), since is known that competitive interactions are stronger among individuals of similar body sizes (Santos-Filho, 1997;Canavero et al, 2013;Ortiz & Arim, 2016).…”

“…The ontogenetic changes in diet between size classes of C. fulgens might occur as a consequence of the increase in body size (Arim et al, 2010), and not as a response for minimize intraspecific competition in this studied population. We believe that the most important morphological changes during C. fulgens ontogeny are the increase of the mouth gape limitation (Keenleyside, 1979;Magnan & FitzGerald, 1984), handling efficiency of prey items (Xue et al, 2005) and swimming ability (Wootton, 1999;Ward et al, 2006;Keppeler et al, 2015), allowing the consumption of a variety of food items, larger prey items and with a higher caloric content (Abelha et al, 2001;Arim et al, 2010). This can be interpreted in light of the theory of optimal foraging, which predicts that foragers should select prey items for optimizing their energy intake in relation to the costs of catching, ingesting and digesting these preys (Pyke et al, 1977;Werner & Gilliam, 1984;Gerking, 1994;Wainwright & Richard, 1995).…”

“…Despite the large diversity of the Cynolebiidae family (Costa, 2008) and the vulnerability of some species Rosa & Lima, 2008), ecological characteristics such as feeding, reproduction, behavior patterns, growth, species richness and abundance of annual fishes in temporary environments are poorly known (Arenzon et al, 1999(Arenzon et al, , 2001(Arenzon et al, , 2002Errea & Danulat, 2001;Shibatta & Rocha, 2001;Shibatta, 2005Shibatta, , 2006García et al, 2008;Laufer et al, 2009;Arim et al, 2010;Gonçalves et al, 2011;Canavero et al, 2013;Lanés et al, 2013Lanés et al, , 2014aLanés et al, , b, 2016Keppeler et al, 2013Keppeler et al, , 2015Ortiz & Arim, 2016).…”

“…Studies on C. fulgens covering aspects of life history, embryonic development and toxicity have been conducted in a temporary water body in Tramandaí (RS) (Arenzon et al, 1999(Arenzon et al, , 2001(Arenzon et al, , 2002(Arenzon et al, , 2003 and in temporary ponds in Parque Nacional da Lagoa do Peixe (RS) (Lanés et al, 2014b(Lanés et al, , 2016. However, to our knowledge, there is only a few information on the trophic ecology of this species (Keppeler et al, 2013(Keppeler et al, , 2015..…”

“…The feeding abilities frequently change during the fish ontogeny, mainly due to modifications in body characteristics that could determine physical restrictions on the prey size and consequent feeding selectivity (Wainwrigth & Richard, 1995;Arim et al, 2010;Keppeler et al, 2013Keppeler et al, , 2015. Changes in feeding resources choices could indicate that a species belongs to different trophic niches in specific phases of its ontogeny (Rezsu & Specziár, 2006).…”