Bilateral Song Convergence in a Passerine Hybrid Zone: Genetics Contribute in One Species Only

Abstract

Hybridization can drive the convergence of territorial and sexual signals. However, non-genetic processes such as competition, environment matching, or cultural transmission, also generate this pattern. We investigated the effect of hybridization on song convergence between two interspecifically territorial warblers in a moving hybrid zone. We confirmed song convergence in each species. Using an AFLP-based genetic index, we detected an effect of genetics on song convergence in Hippolais polyglotta, the expanding species. Evidence was weaker for H. icterina, the receding species. In moving zones, introgression is expected to be larger in the expanding species than in the receding. Thus, the asymmetric contribution of the genetic index to convergence was consistent with expectations for genetically determined traits in moving hybrid zones, and the observed introgression pattern of AFLP markers. However, the geographical location of individuals had an effect on song variation too when genetics was accounted for, suggesting that convergence also has non-genetic explanations. We examine the possible role of alternative processes to that of hybridization and discuss their conflicting effects on reinforcement and hybrid zone dynamics.

Reproductive character displacement of female, but not male song discrimination in an avian hybrid zone

“…As a result, the songs of males from the less numerous/aggressive species may be under selective pressure to converge and, correspondingly (e.g., Secondi et al. ), their song discrimination may be selected to weaken (Pearson and Rohwer ). In line with this prediction, song discrimination in male collared flycatchers was stronger in sympatry than that of male pied flycatchers and, moreover, there was a trend for song recognition in male pied flycatchers to be wider in sympatry (Fig.…”

The Causes and Evolutionary Consequences of Mixed Singing in Two Hybridizing Songbird Species (Luscinia spp.)

“…Such mechanisms are expected to result in quantitative changes in temporal or frequency parameters of the song [14], [16], [20], [69]. They are, however, unlikely to cause acquisition of completely different song types, as happens in nightingales.…”

“…[8], [23] and warblers Hippolais spp. [20], [33]. The results of these studies indicate that several of the mechanisms mentioned above may contribute to this phenomenon in different species; however, the evolutionary consequences, effects on the speciation process, and a potential adaptive value of song convergence remain poorly understood.…”

“…On the other hand, species may also converge in some features; this is often observed in bird songs (e.g., [6], [11]). The mechanisms leading to song convergence may include (1) cross-species song learning [3], [12], [13], (2) ecological adaptation to the local environment [14]–[17], and (3) genetic introgression [18]–[20]. Such convergence can be followed by broad heterospecific pairing, resulting in increased interspecific hybridization and mixing of species gene pools [21]–[23].…”

Reproductive interference via display signals: the challenge of multiple receivers

“…Signal convergence has been especially well documented in the songs of syntopic songbirds (oscine passerines), a phenomenon referred to as mixed singing when convergence occurs through incorporation of typical heterospecific song elements (Helb et al 1985). One explanation for mixed song is that it is a non-adaptive byproduct of an open song-learning process otherwise promoted by sexual selection on repertoire size (Helb et al 1985;Secondi et al 2011;Vokurková et al 2013). According to this view, a general female preference for elaborated songs overrides any costs to mixing.…”