Landscape and demographic history shape current leopard cat population structure in Taiwan
Our analysis of colonization history revealed a divergence between the Northern and Southern populations 800 years ago, followed by a secondary contact 200 years ago. We infer that this secondary contact generated the diversity hotspot and the pattern of admixture observed in the Central population. Although the exact cause of this secondary contact remains unclear, historical climate fluctuations and human activities are likely contributing factors. Similar demographic changes in other mammals have been attributed to climate variations and human disturbances (Ding et al., 2011; Haffer, 1969; Lavretsky et al., 2020; Perry et al., 2001). We also found evidence of bottleneck events in the past 200 years, coinciding with rapid human development in Central Taiwan (Barclay, 2015; Wu, 2004). Habitat loss, deforestation, and changes in land cover to residential or commercial use have negatively impacted several species in Taiwan, including leopard cats (Chang et al., 2012; Hwang et al., 2010; Karczmarski et al., 2017). Consequently, the distribution of leopard cats has significantly declined, with their occurrence now limited to central Taiwan (Chen, 1956; Horikawa, 1931). Our genetic analyses support the notion that intense anthropogenic impacts have contributed to the reduction in effective population sizes of the island’s leopard cats.
In landscape genetic studies, it is challenging to interpret how contemporary landscapes and historical demographic processes influence genetic structure and gene flow due to the time lag problem (Bolliger, Lander, & Balkenhol, 2014; Epps & Keyghobadi, 2015). Various molecular markers and approaches have been used to assess the effects of contemporary landscapes and historical events on genetic structures at different timescales (Epps & Keyghobadi, 2015), with one such approach being to combine genetic markers displaying different mutation rates (Pérez-Espona, McLeod, & Franks, 2012). Although our mtDNA data could not provide insights into historical events, we were able to apply a variety of statistical techniques on the nuclear loci, combining landscape genetic analyses and coalescent methods (Epps & Keyghobadi, 2015). By doing so, we revealed associations between current landscape features and population structures, with historical evolutionary events also contributing to the genetic profile of leopard cats. Nevertheless, quantifying and distinguishing the relative importance of historical and contemporary factors in shaping genetic structure is difficult, especially when multiple potential explanations are correlated or non-exclusive (Shirk, Landguth, & Cushman, 2018). However, the high mutation rates of microsatellite markers can still effectively reflect barriers or fragmentation caused by current landscapes or anthropogenic constructions, particularly when the focal species has a short generation time and the barriers have existed for a long time (Epps & Keyghobadi, 2015; Shirk, Landguth, & Cushman, 2018; Wang, 2011).