Résumé
Evolutionary radiations are considered key processes underlying the origin
of biodiversity. Notably, the mechanisms driving these radiations can vary
across organisms and often involve a complex interplay of abiotic and
biotic factors. Empirical studies on evolutionary history are crucial for
validation of multiple hypothesis regarding the mode of evolutionary
radiations. Within the obligatory aquatic insect order Megaloptera, the
genus Protohermes is the most speciose clade with 90 described species,
accounting for around 22 % of the total ordinal diversity. Protohermes
species are featured by the limited dispersal ability, primarily occurring
across the Oriental region, and a range of diversified phenotypes, e.g.,
highly divergent genital characters, and mimetic coloration alongside
shifts in biological rhythm—from nocturnal to diurnal activities. Here, we
infer the spatiotemporal mode of diversification and associated driving
factors of the Protohermes radiation as a test case for exploring the
processes and potential mechanisms of evolutionary radiations. We present
the first time-calibrated phylogeny of Protohermes using genome-scale data
of ultraconserved elements (UCEs) and mitochondrial genes with a
comprehensive taxon sampling. Our results reveal a mid-Cretaceous stem age
of Protohermes, followed by a recent and steady diversification during the
Neogene. Estimation of historical biogeography suggests the genus likely
originated from a broad range including the Himalaya-Hengduan Mountains +
Indochina + Borneo, with the first two areas serving as the center of
early diversification. Our results further suggest that vicariance events,
likely attributed to the Cenozoic Himalayan orogeny as well as climate
change in East Asia, triggered speciation that coincided with the
accumulation of genital divergence. Further enhancement of genital and
phenotypic diversification may have been promoted by secondary contacts of
allopatric or parapatric lineages following the build-up of species
richness, likely facilitating species coexistence and lineage
accumulation. We argue that the current species diversity of Protohermes
likely resulted from a non-adaptive radiation. Our results highlight the
role of geographic vicariance and sexual selection in driving the species
and phenotypic diversification in insects.