Montane speciation
The information gathered with the present genomic data and current
distribution recovered a phylogeographic pattern that can be associated
with the São Paulo subtropical gap (sensu Amaral et al., 2021),
as a phylogeographic break for these montane butterflies. The role of
the Atlantic Forest Mountain ranges in shaping the genetic structure of
endemic species has already been observed for birds (Amaral et al.,
2021; Thom et al., 2020). However, this is the first time that this
pattern has been reported for an invertebrate. A previous study with the
cold-associated bumblebees Bombus morio and B. pauloensis ,
which are mainly found in high- altitude areas of MAF, failed to recover
a strong structured phylogeographic pattern (Françoso et al., 2016).
However, the results of the demographic analyses and paleodistribution
models are consistent with a scenario of expansion during the LGM.
The speciation between A. alalia and A. mantiqueiraprobably occurred recently during the Quaternary, considering that the
divergence between these species and its sister species, A.
catarina , was estimated around 3 million years ago, at the end of the
Pliocene (Magaldi et al. in prep.). Pleistocene climatic oscillations
have been hypothesized to have shaped the genetic structure of
populations of other species currently found on the MAF (Amaral et al.,
2021; Françoso et al., 2016; Thom et al., 2020). Our results are
consistent with paleoclimate, molecular, and pollen data obtained for
other species, suggesting that the MAF taxa persisted or expanded during
the LGM (Amaro et al., 2012; Carnaval et al., 2009; Leite et al., 2016).
Accordingly, the ancestral populations of A. alalia and A.
mantiqueira may have been limited to mountain tops several times in the
past, yet they were likely able to explore currently unsuitable regions
(mostly lowland) and hence expand their distribution during colder
periods, which could have enabled a dispersal process to new mountain
ranges (Paz et al., 2019). Mountain ranges provide diverse climatic
conditions that allow montane species to adapt and survive the
fluctuations in climate. This is made possible by the extensive variance
in topography and altitudinal gradients (Brown Jr. & Ab’Saber, 1979).
Furthermore, the low levels of genetic differentiation (as estimated by
FST values) between the populations may not be due to
high levels of current gene flow, but rather to this recent divergence
(Palsbøll et al., 2004). Combining molecular and niche modeling data, we
propose that Pleistocene climatic variation led to an allopatric and
recent speciation process between the mountains of the Atlantic Forest.