The effect of long-term historical habitat fragmentation on genetic diversity of the relictual conifer Calocedrus macrolepis (Cupressaceae) in China

Abstract

Geological events and glacial history have all induced habitat fragmentation, which has long been recognized as a major threat to the survival of many species. However, fragmentation has differential effects on population genetic patterns of individual species, such as loss of genetic diversity, genetic differentiation enhance, inbreeding increase, allelic deletion, and no effect. Calocedrus macrolepis Kurz is an endangered ancient relictual and fragmented conifer. In this study, the genetic diversity and structure were analyzed to shed light on the factors that determine their contemporary genetic patterns and to provide optimum strategies for future conservation. The genetic diversity within and among 14 extant populations of C. macrolepis was analyzed using nine microsatellite markers. The genetic diversity (H E = 0.636), genetic differentiation (F ST = 0.163), and gene flow (Nm = 1.496) were disclosed, respectively. No significant correlation was detected by the Mantel test between genetic and geographical distances among pair-wise comparisons of populations (r = 0.197, P = 0.103). Fourteen populations could be generally assigned to two separate groups, and significant asymmetrical migration among populations within the regional groups was revealed. Both Quaternary glaciations and neotectonic movements seem to be associated with a long history of population contraction and fragmentation of C. macrolepis, enhancing its genetic drift and population divergence. The results indicate that longterm habitat fragmentation could be responsible for the genetic structure observed. In situ conservation strategies should be designed, especially small and isolated populations. Also, special attention should be given to populations LY and DZ because of their private alleles, as well as to population CJ isolated from the mainland.

Distinct Genetic Structure Reflects Ploidy Level Differentiation in Newly Discovered, Extremely Small Populations of Xanthocyparis vietnamensis from Southwestern China

“…Our population genetic survey revealed moderate genetic differentiation (F ST 0.125) among X. vietnamensis populations in southwestern China. This is similar to the mean values of anemochores (0.13) (Nybom, 2004), lower than those of F.hodginsii (0.157) (Yin et al, 2018), C. macrolepis (0.163) (Liao et al, 2015), A. ziyuanensis (0.209-0.250) (Tang et al, 2008), and G. pensilis (0.452, some populations are plantations) (Wu et al, 2020) in a similar geographic region. Varied topography of mountain regions in the tropic and adjacent areas tended to harbor Tertiary relict species and subdivide some species into isolated and divergent populations, which may have evolved independently during late Tertiary climate changes and Quaternary climate fluctuations (Hewitt, 2000;Tang et al, 2018).…”

“…Many species of conservation concern are endemic, fragmented, and have limited gene flow and high level genetic differentiation among populations, which are generally attributed to cyclical climatic changes, complex geological history, and longstanding influence of human activities ( González-Martínez et al, 2010 ; Liao et al, 2015 ; Li et al, 2020 ). Usually, high levels of endemism suggests in situ long-term survival, differentiation, and speciation ( Tang 2015 ).…”

“…Fragmentation of habitats is usually accompanied by reductions in population size, genetic isolation, increased inbreeding within populations, and decreases in genetic diversity ( Aguilar et al, 2008 ). Hence, habitat fragmentation is considered one of the biggest threats to the survival of species with small and isolated populations, especially in the context of increased intensity of human activities all over the world ( Hamrick, 2004 ; Liao et al, 2015 ). It is imperative to investigate the effect of habitat fragmentation on endangered relict plants.…”

Pronounced genetic differentiation in Fokienia hodginsii revealed by simple sequence repeat markers

“…Genetic diversity plays an important role in determining the survival and adaptability of a species (Liao et al, ). The high genetic diversity maintained within F. hodginsii and the initial significant genetic differentiation among its populations found in this study are encouraging.…”

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“…These regions have drawn significant attention from researchers. Conservation genetic studies have been conducted for many threatened plant species, such as Calocedrus macrolepis and Fokienia hodginsii (Liao et al, 2015;Yin et al, 2021), yet no population genetic survey has been done for X. vietnamensis. Characterizing the genetic variation in populations of X. vietnamensis is essential for effective conservation.…”