Host specialist clownfishes are environmental niche generalists

Abstract

Why generalist and specialist species coexist in nature is a question that has interested evolutionary biologists for a long time. While the coexistence of specialists and generalists exploiting resources on a single ecological dimension has been theoretically and empirically explored, biological systems with multiple resource dimensions (e.g. trophic, ecological) are less well understood. Yet, such systems may provide an alternative to the classical theory of stable evolutionary coexistence of generalist and specialist species on a single resource dimension. We explore such systems and the potential tradeoffs between different resource dimensions in clownfishes. All species of this iconic clade are obligate mutualists with sea anemones yet show interspecific variation in anemone host specificity. Moreover, clownfishes developed variable environmental specialization across their distribution. In this study, we test for the existence of a relationship between host-specificity (number of anemones associated with a clownfish species) and environmental-specificity (expressed as the size of the ecological niche breadth across climatic gradients). We find a negative correlation between host range and environmental specificities in temperature, salinity and pH, probably indicating a trade-off between both types of specialization forcing species to specialize only in a single direction. Trade-offs in a multi-dimensional resource space could be a novel way of explaining the coexistence of generalist and specialists.

Forecasting pollination declines through DNA barcoding: the potential contributions of macroecological and macroevolutionary scales of inquiry

“…range and population size) and may therefore fail to capture the functional role of a species (i.e. such habitat specialists are often diet generalists; Litsios et al, 2014). By necessity, specialization is often considered a relatively invariant species-property that is consistent across locations (Devictor et al, 2010).…”

Niche width impacts vertebrate diversification

“…However, relatively few studies have attempted to describe the evolutionary history of the niche width at the macroevolutionary scale, and we are currently lacking a clear understanding of the evolution of the niche width and its potential effects on the rates of species diversification (i.e. speciation and extinction rates; but see Kostikova et al, ; Litsios et al ., ; Gómez‐Rodríguez et al ., ).…”

Evolutionary ecology of specialization: insights from phylogenetic analysis

“…Examining these trade-offs in a phylogenetic framework can be a powerful approach to understanding the constraints on the evolution of specialization. Litsios et al [52] provide evidence in this Special Feature of a negative correlation between environmental tolerances (in temperature, salinity and pH) and host specificities in clownfish and anemone mutualisms, which would likely confound phylogenetic analyses of diversification along any single specialization niche axis. Further, if differential specialization across resource axes is widespread, it may be a large contributor to the local coexistence of specialist and generalist species [52], and provide insight into the puzzling observation that specialists often do not outcompete generalists [53].…”

“…networks tend to be asymmetrical and nested) [70,71]. Second, as exemplified in clownfish in this Special Feature, generalist-specialist trade-offs across multiple resource axes will act as a buffering force, such that specialists in bipartite networks may be habitat generalists, thus providing a further balancing mechanism that allows for coexistence of species [52]. Recent studies have incorporated macroevolutionary and phylogenetic approaches into network studies to reveal the influence of shared traits on forming network interactions [28,64], and the new metrics currently emerging [72] will likely further provide an important link between the influences of evolutionary history, traits, and environmental heterogeneity.…”