Competition and phylogeny determine community structure in Müllerian co-mimics

Abstract

Until recently, the study of negative and antagonistic interactions (for example, competition and predation) has dominated our understanding of community structure, maintenance and assembly. Nevertheless, a recent theoretical model suggests that positive interactions (for example, mutualisms) may counterbalance competition, facilitating long-term coexistence even among ecologically undifferentiated species. Müllerian mimics are mutualists that share the costs of predator education and are therefore ideally suited for the investigation of positive and negative interactions in community dynamics. The sole empirical test of this model in a Müllerian mimetic community supports the prediction that positive interactions outweigh the negative effects of spatial overlap (without quantifying resource acquisition). Understanding the role of trophic niche partitioning in facilitating the evolution and stability of Müllerian mimetic communities is now of critical importance, but has yet to be formally investigated. Here we show that resource partitioning and phylogeny determine community structure and outweigh the positive effects of Müllerian mimicry in a species-rich group of neotropical catfishes. From multiple, independent reproductively isolated allopatric communities displaying convergently evolved colour patterns, 92% consist of species that do not compete for resources. Significant differences in phylogenetically conserved traits (snout morphology and body size) were consistently linked to trait-specific resource acquisition. Thus, we report the first evidence, to our knowledge, that competition for trophic resources and phylogeny are pivotal factors in the stable evolution of Müllerian mimicry rings. More generally, our work demonstrates that competition for resources is likely to have a dominant role in the structuring of communities that are simultaneously subject to the effects of both positive and negative interactions.

Two new species of Corydoras Lacépède, 1803 (Siluriformes: Callichthyidae) from the rio Madeira basin, Brazil

“…Vertebral counts include only free centra, with the compound caudal centra (preural 1+ ural 1) counted as a single element. Terminology of snout external morphology follows Alexandrou et al (2011). In the description and diagnosis, the dark longitudinal stripes were counted only when well defined, continuous and not fused to the blackened dorsal portion of the fish's body.…”

“…Corydoras brittoi can be distinguished from all of its congeners, with exception of the species from 'lineage 8' sensu Alexandrou et al (2011), by the presence of posterior margin of dorsal-fin spine with laminar serrations directed towards the origin of the spine (vs. serrations, when present, conical; directed towards dorsal-fin spine tip in the members of the remaining lineages). Corydoras brittoi can be distinguished from other members of 'lineage 8', with exception of C. bifasciatus Nijssen, 1972, C. pinheiroi Dinkelmeyer, 1995 andC.…”

“…During a recent field expedition in the rio Aripuanã and its tributaries in the rio Madeira basin, two new species with similar color pattern but showing divergent snout morphology were found. In this paper, we describe these two sympatric and syntopic species and demonstrate that although they have similar color pattern, they belong to clearly distinct morphological groups that correspond to different lineages sensu Alexandrou et al (2011).…”

“…Efforts to understand the taxonomy and systematics of Corydoras have included Ellis (1913), Gosline (1940), , , Britto (2003) and Alexandrou et al (2011). Multiple studies have noted apparent cases of convergence of color pattern in Corydoras.…”

“…Based on phylogenetic analyses, Britto (2003) noted another case of apparent color convergence involving Corydoras nattereri Steindachner, 1876 in the Corydoras clade and C. prionotos in the Scleromystax clade. Alexandrou et al (2011) study of community structure in Corydoradinae was the first paper to explicitly hypothesize an adaptive basis for the convergence of color patterns in Corydoras. The study was based on a molecular phylogenetic analysis that established nine well-defined clades -each with characteristic snout morphology.…”