Convergent evolution of bird-mammal shared characteristics for adapting to nocturnality

Abstract

The diapsid lineage (birds) and synapsid lineage (mammals), share a suite of functionally similar characteristics (e.g. endothermy) that are considered to be a result of their convergent evolution, but the candidate selections leading to this convergent evolution are still under debate. Here, we used a newly developed molecular phyloecological approach to reconstruct the diel activity pattern of the common ancestors of living birds. Our results strongly suggest that they had adaptations to nocturnality during their early evolution, which is remarkably similar to that of ancestral mammals. Given their similar adaptation to nocturnality, we propose that the shared traits in birds and mammals may have partly evolved as a result of the convergent evolution of their early ancestors adapting to ecological factors (e.g. low ambient temperature) associated with nocturnality. Finally, a conceptually unifying ecological model on the evolution of endothermy in diverse organisms with an emphasis on low ambient temperature is proposed. We reason that endothermy may evolve as an adaptive strategy to enable organisms to effectively implement various life-cycle activities under relatively low-temperature environments. In particular, a habitat shift from high-temperature to relatively low-temperature environments is identified as a common factor underlying the evolution of endothermy.

Keywords: endothermy; habitat shift; low temperature; nocturnality.

Figure 1.

Diel activity pattern reconstruction. The phylogenetic relationships of species used in this study follows published literature [–36] and the Tree of Life Web Project (http://tolweb.org/Passeriformes). The diel activity classification of taxonomic bird orders follows one published study [16]. Red shows bird orders involved in nocturnal and/or crepuscular activities. Except for five regularly nocturnal bird groups, which harbour mainly nocturnally active species, all other bird groups are considered as typically diurnal, but widely show occasional nocturnality or engage in partial behaviours during crepuscular periods [16].

Figure 2.

Reconstructed diel activity patterns of main groups of amniotes based on the results of this study and previous studies [13,45]. Living endothermic groups and their possible early evolution of endothermy are shown in red based on previous studies [,–51].

Figure 3.

Integrated evolution of bird-mammal shared characteristics for adapting to nocturnality. Arrows show possible cause and effect relationships between two nocturnality-associated selection pressures (visual constraints and low temperature) and the evolution of BMSC. Please see text for details. The black background represents dim-light environments (e.g. night) and red represents the evolution of endothermy-related characteristics under low-temperature selection pressure. BMR, basal metabolic rate.