Diving into a dead-end: asymmetric evolution of diving drives diversity and disparity shifts in waterbirds

Abstract

Diving is a relatively uncommon and highly specialized foraging strategy in birds, mostly observed within the Aequorlitornithes (waterbirds) by groups such as penguins, cormorants and alcids. Three key diving techniques are employed within waterbirds: wing-propelled pursuit diving (e.g. penguins), foot-propelled pursuit diving (e.g. cormorants) and plunge diving (e.g. gannets). How many times diving evolved within waterbirds, whether plunge diving is an intermediate state between aerial foraging and submarine diving, and whether the transition to a diving niche is reversible are not known. Here, we elucidate the evolutionary history of diving in waterbirds. We show that diving has been acquired independently at least 14 times within waterbirds, and this acquisition is apparently irreversible, in a striking example of asymmetric evolution. All three modes of diving have evolved independently, with no evidence for plunge diving as an intermediate evolutionary state. Net diversification rates differ significantly between diving versus non-diving lineages, with some diving clades apparently prone to extinction. We find that body mass is evolving under multiple macroevolutionary regimes, with unique optima for each diving type with varying degrees of constraint. Our findings highlight the vulnerability of highly specialized lineages during the ongoing sixth mass extinction.

The neck as a keystone structure in avian macroevolution and mosaicism

“…Rate shifts are most frequently found in aquatic feeding and arboreal gleaning birds, both of which are niches that require extensive morphological adaptations across the entire body. The avian transition from land to water has involved a myriad of adaptations across the body to allow birds to effectively move through water [ 13 , 46 – 48 ], a medium that is many times denser than air. Adaptations of the avian wing to a life aquatic have been well documented [ 41 , 46 , 47 ], and significant rate shifts of distal forelimb morphology have been observed at the base of Sphenisciformes + Procellariiformes [ 47 ].…”

“…The avian transition from land to water has involved a myriad of adaptations across the body to allow birds to effectively move through water [ 13 , 46 – 48 ], a medium that is many times denser than air. Adaptations of the avian wing to a life aquatic have been well documented [ 41 , 46 , 47 ], and significant rate shifts of distal forelimb morphology have been observed at the base of Sphenisciformes + Procellariiformes [ 47 ]. Penguins display a highly modified neck that is able to provide strong, fast movements of the head to capture prey whilst keeping the head close to the body [ 49 ].…”

“…3 A). By capitalizing on preexisting phenotypic covariance, penguins were able to evolve a neck morphology that allows them to participate in a novel and specialized foraging strategy, wing-propelled pursuit diving [ 46 ]. Similar to the land-to-water transition, the niche shift from ground foraging to arboreal gleaning necessitated the evolution of cranial, appendicular and axial morphological adaptations [ 51 , 52 ].…”

How an Age-Old Photo of Little Chicks Can Awaken Our Conscience for Biodiversity Conservation and Nature Protection

“…This is particularly significant as human activities directly impact the loss of wild natural habitats, greenhouse gas emissions cause temperature fluctuations and disturb wildlife's long-standing growth conditions, and destructive exploitation of nature still occurs at an alarming rate (Armstrong McKay et al, 2022;Cooke et al, 2023). For species sensitive to environmental changes like the kingfisher, temperature fluctuations and alternations in growth conditions pose a higher risk of extinction for some critically endangered kingfisher species (Barik et al, 2022;Shifa et al, 2023;Tyler & Younger, 2022).…”

Diving to extinction: Water birds at risk

“…Great Blue Heron, taken by Russ Hartung. Retrieved from: https://www.audubon.org /news/audubon-members-wade-through-memories-their-favorite-water-birds A recent study published in Proceedings of the Royal Society B discovered that diving has been acquired independently at least 14 times in waterbirds, but there were no instances of diving birds reversed into the non-diving forms [2]. The analysis was conducted on a collection of 727 waterbird species across 11 bird groups.…”