High frequency of apomixis in subterranean islands challenges macro-climatic models of geographical parthenogenesis

The Geographical Parthenogenesis (GP) hypothesis traditionally links apomixis to high-latitude and alpine regions, driven by a combination of thermal stress, UV radiation, and pollination barriers. At the core of the GP hypothesis is Baker’s Law, which asserts the evolutionary advantage of autonomous reproduction during the colonization of isolated habitats, frequently linking this advantage to macro-climatic stress. By investigating reproductive modes in subtropical subterranean karst caves, we test the core assumption that macro-climatic stress is the primary driver of apomixis. Our results suggest that barriers to pollination drive a high frequency of apomixis independently of thermal stress or UV radiation. Furthermore, we find a complete phylogenetic turnover between high-elevation, open, apomict-rich habitats and mid-elevation cave environments. Taxonomic composition in these caves is dictated by pre-adaptations to deep shade combined with a lineage-specific predisposition for autonomous reproduction. We propose that the GP hypothesis may be overly influenced by habitat sampling bias. Broader, unbiased sampling could yield a more nuanced and predictive framework to explain variations in apomixis frequency, ultimately providing deeper insights into the role of asexual reproduction in evolution.