A latitudinal gradient in rates of evolution of avian syllable diversity and song length

Abstract

We ask whether rates of evolution in traits important for reproductive isolation vary across a latitudinal gradient, by quantifying evolutionary rates of two traits important for pre-mating isolation-avian syllable diversity and song length. We analyse over 2500 songs from 116 pairs of closely related New World passerine bird taxa to show that evolutionary rates for the two main groups of passerines-oscines and suboscines-doubled with latitude in both groups for song length. For syllable diversity, oscines (who transmit song culturally) evolved more than 20 times faster at high latitudes than in low latitudes, whereas suboscines (whose songs are innate in most species and who possess very simple song with few syllable types) show no clear latitudinal gradient in rate. Evolutionary rates in oscines and suboscines were similar at tropical latitudes for syllable complexity as well as for song length. These results suggest that evolutionary rates in traits important to reproductive isolation and speciation are influenced by latitude and have been fastest, not in the tropics where species diversity is highest, but towards the poles.

Distinct song parts of the endemic marsh grassbird of China vary with latitude and climate among migratory and sedentary populations

“…The duration of the warble part was positively correlated with latitude, which is in line with expected elaboration in more seasonal and unpredictable habitat with presumable stronger sexual selection pressures (c.f. Catchpole 1982;Irwin 2000;Botero et al 2009;Weir and Wheatcroft 2011). However, at the same time we found the number of different element types of the warble part to be negatively correlated with latitude.…”

“…Sedentary populations may also have more convergent songs through copying of neighbourhood songs, at least in some species, driven by the higher consistency in the identity of neighbouring males (Kroodsma 1999). Furthermore, variation in habitat density and species diversity may yield variable competition for acoustic space, and thereby allow song elaboration more easily at relatively high latitudes, where vegetation is typically less dense and acoustic competition with other species less intense (Weir and Wheatcroft 2011;Singh et al 2015). Several comparative studies have confirmed positive correlations between song elaboration and latitude, both among (Catchpole 1982;Botero et al 2009) and within species (Collins et al 2009;Kaluthota et al 2016).…”

“…We included rainfall and temperature, which are well-known to affect migratory behaviour (Salewski and Bruderer 2007;Louchart 2008;Zink 2011) and possibly song structure (e.g. Botero et al 2009;Weir and Wheatcroft 2011;Medina and Francis 2012). We explored whether the acoustic variation within songs and across latitude and climate was in line with expectations for divergent functions of the different song parts.…”

The relationship between latitude, migration and the evolution of bird song complexity

“…Irwin 2000, Mahler & Gil 2009, Weir & Wheatcroft 2011, Cardoso et al 2012; Table 1). Hypotheses proposed to explain this variation invoke both ecological selection (Weir et al 2012) and sexual selection (Catchpole 1982) as the causes of these patterns (Table 2).…”

Migration and song elaboration in wood-warblers (Geothlypis)

“…In the years since Catchpole (1982) hypothesized that migratory songbird species might be expected to sing more elaborate songs than nonmigratory species, several broad comparative studies have found a positive association between song elaboration and migratory distance (Read andWeary 1992, Mountjoy andLeger 2001) or breeding latitude (Botero et al 2009, Mahler and Gil 2009, Weir and Wheatcroft 2011, Cardoso et al 2012, Greig et al 2013). These empirical findings are intriguing, but they are also puzzling, because it is not clear why migration and song elaboration would be linked.…”