Emerging pathogens: fungal host jumps following anthropogenic introduction.

an important additional dimension. In birds, sexual dimorphism in singing and song learning varies greatly among species, and sex differences in brain morphology are the most extreme documented in any vertebrate [2,3]. Differences in female song-learning strategies might be even greater than those observed in male vocal learning, ranging from no learning to learning as much as males do [3,4]. Similar to males, individual females also vary in song complexity [5] and sharing levels [6,7]. In reviewing the functional basis of different song-learning strategies, the authors group Repertoire hypotheses , which suggest learning is advantageous where female preferences select for larger repertoires, and Sharing hypotheses, which suggest that learning songs shared with neighbours leads to selective advantage. Neither hypothesis considers female song [4,5,8] or learned song preferences [4]. The authors limit the role of females to selecting for increased male repertoire size (a preference that could result from unlearned biases). However, to identify the selection pressures on song learning, female singing and learned song preferences need to be incorporated. The study of female song offers additional advantages in this respect. Not only is interspecific variation in female song learning extreme, but in many species female song production is also restricted to certain social and ecological contexts (e.g. shortage of nest sites, or facultative polygyny) [5]. This high degree of inter-and intraspecific variation facilitates the isolation of the ecological and social factors that favour particular learning strategies. We would like to stimulate the discussion further by postulating that, given the probable Australasian origin of oscine passerines [9] and the prevalence of female song in Australian birds [10], song in both sexes could be the ancestral condition. The real challenge for phylogenetic analyses might be to identify the factors that made it advantageous for females to give up singing. 'Song phylogenies' need to consider sex differences nested within species, and the coevolution between learned male song and learned female preference [4]. We support Beecher and Brenowitz in their quest to initiate comparative and phylogenetic analyses of song learning, but suggest that further insight can be gained through investigation of the poorly understood song-learning strategies of females. Interspecific comparisons of the size of neural song control regions and song complexity in duetting birds: evolutionary implications. The 'mute' sex revisited: vocal production and perception learning in female songbirds. Sex differences in singing and duetting behavior of neotropical rufous-and-white wrens. Auk 122, 175–186 7 Mennill, …