Convergent evolution in social swallows (Aves: Hirundinidae)

Abstract

Behavioral shifts can initiate morphological evolution by pushing lineages into new adaptive zones. This has primarily been examined in ecological behaviors, such as foraging, but social behaviors may also alter morphology. Swallows and martins (Hirundinidae) are aerial insectivores that exhibit a range of social behaviors, from solitary to colonial breeding and foraging. Using a well‐resolved phylogenetic tree, a database of social behaviors, and morphological measurements, we ask how shifts from solitary to social breeding and foraging have affected morphological evolution in the Hirundinidae. Using a threshold model of discrete state evolution, we find that shifts in both breeding and foraging social behavior are common across the phylogeny of swallows. Solitary swallows have highly variable morphology, while social swallows show much less absolute variance in all morphological traits. Metrics of convergence based on both the trajectory of social lineages through morphospace and the overall morphological distance between social species scaled by their phylogenetic distance indicate strong convergence in social swallows, especially socially foraging swallows. Smaller physical traits generally observed in social species suggest that social species benefit from a distinctive flight style, likely increasing maneuverability and foraging success and reducing in‐flight collisions within large flocks. These results highlight the importance of sociality in species evolution, a link that had previously been examined only in eusocial insects and primates.

Phylogenetic convergence and multiple shell shape optima for gliding scallops (Bivalvia: Pectinidae)

“…The recent development of quantitative, pattern‐based evolutionary convergence tests finally provides us with a useful set of tools to evaluate convergence within a phylogenetic context (Stayton, ). This approach has been used successfully to quantify convergent evolution across ecological guilds in a wide variety of taxa including pythons and boas (Esquerré et al ., ), planktivorous surgeonfishes (Friedman et al ., ), social swallows (Johnson et al ., ) and squirrels (Zelditch et al ., ). Thus, the application of quantitative measures should illuminate convergence patterns in understudied taxa and provide key evidence in determining the extent to which independent lineages converge on a common phenotype or display a suite of closely related solutions to similar ecological challenges.…”

Sexually dimorphic swallows have higher extinction risk

“…Using a phylogenetic comparative analysis, we first studied the relationship between sexual plumage dimorphism (in all plumage‐based characteristics) and extinction risk. Then, because long tails have been acquired and lost repeatedly in this clade (Johnson, Mitchell, & Brown, ), and because long tails are well‐known sexually selected traits at least in the barn swallow H. rustica (see above), we also determined whether sexual tail dimorphism explained extinction risk. Hirundines are affected great deal by environmental changes, because they require adequate weather to feed (e.g., heavy rain, drought, and cyclone lead to population decline, population crash, and large‐scale mortality; reviewed in Turner & Rose, ).…”

Why the long beak? Phylogeny, convergence, feeding ecology, and evolutionary allometry shaped the skull of the Giant Cowbird Molothrus oryzivorus (Icteridae)

“…According to our estimates with the indices of Stayton (2015), the Giant Cowbird is highly convergent with sampled caciques and oropendolas in skull shape, particularly with the Yellow‐rumped Cacique (host of the Giant Cowbird; Lowther, 2016). In the latter case, evolution brings them closer a 78.5% of their maximum ancestral distance, an extremely high amount of convergence when compared to estimates in different groups of birds (Johnson et al, 2017), lizards (Gray et al, 2019), and mammals (Grossnickle et al, 2020). This extreme convergence is further stressed by the unique nature of their skulls among icterids, which is reflected by their occupation of an otherwise unexplored region of the morphospace, but also by the long branches leading to them (Figure 6).…”