Introgression occurs
https://www.authorea.com/users/447785/articles/546727-integrative-taxonomy-of-two-thrush-complexes-aves-turdidae-reveals-introgression-across-sister-speciesmore frequently among birds than in mammal species
(Grant and Grant, 1992; Mallet, 2005). It has been reported that more
than 9% of birds have undergone introgression, and the proportion of
introgression among birds worldwide may be higher (Grant and Grant,
1992; Randler, 2002). These birds include
Larus hyperboreus and
L. argentatus in Iceland (Vigfusdottir et al., 2008),
Aegithalos bonvaloti and
A. fuliginosus in southwestern
China (Wang et al., 2014),
Ammodramus caudacutus and
A.
nelsoni on the northeastern coast of the United States (Walsh et al.,
2016), and
Strix varia and S. occidentalis in western North
America (Hanna et al., 2018). Recently, some studies have shown that
when reconstructing phylogenetic relationships among related species,
introgression might exacerbate nuclear-mitochondrial discordance (Haines
et al., 2017; Kinoshita et al., 2019; Lu et al., 2001; Walsh et al.,
2016). There are several possible hypotheses to explain these phenomena
among birds, such as sex bias (Dai et al., 2013; Toews and Brelsford,
2012), distribution changes (Seixas et al., 2018), and simple stochastic
variation in coalescence times across loci (Phuong et al., 2017;
Rosenberg, 2003).
Turdidae includes approximately 340 species, which are distributed
worldwide. Among these species, 65 are in Turdus (Monroe B.L.,
1993). The classification of several Turdus species, such as the
Naumann’s and dusky thrush complexes and the red-throated and
black-throated thrush complexes, is controversial (Kratter, 2014; Sibley
C.G., 1990). One opinion is that they are two species and four
subspeciee observation of
intermediate specimens between Naumann’s and dusky thrushes (Dong et
al., 2018) and red-throated and black-throated thrushes (Brazil, 2009).
Therefore, an integrative taxonomy of these two thrush complexes is
still necessary.
In the present study, we used
morphological characteristics, including quantitative and qualitative
features, to identify these two thrush complexes and define intermediate
specimens. Using mitochondrial genes and microsatellite loci, we then
analyzed the genetic structure of these two thrush complexes. It was
revealed for the first time that they are sister species with extensive
nuclear introgression.