Evolutionary drivers of the hump-shaped latitudinal gradient of benthic polychaete species richness along the Southeastern Pacific coast

Temporal variations of diversity and community structure of epifauna along the latitudinal and depth gradients in China seas over nearly 60 years

To examine the diversity and community structure of epifauna along latitudinal and depth gradients in China seas and its temporal variations over nearly 60 years, a total of 61,424 records of epifauna were compiled. Latitudinal gradients of γ-diversity from 28 to 37°N showed two peaks of increase in 1958-1960; however, only one peak was observed near 28°N in 2000-2015. Along depth gradient, the peak of species richness shifted about 10 m deeper from about 50 m in 1958-1960 to about 60 m in 2000-2015. Values of α-diversity were higher in 2000-2015 than that in 1958-1960 in latitudes from 30 to 33°N and in depth from 50 to 75 m, respectively. Epifaunal communities were distributed basically along latitudinal and depth gradients. Spatial patterns of communities in the southern Yellow Sea and northern East China Sea were found relatively stable over nearly 60 years.

Global Patterns of Earwig Species Richness

One of the most investigated patterns in species diversity is the so-called latitudinal gradient, that is, a decrease in species richness from the equator to the poles. However, few studies investigated this pattern in insects at a global scale because of insufficient taxonomic and biogeographical information. Using estimates of earwig species richness at country level, their latitudinal diversity gradient was modelled globally and for the two hemispheres separately after correcting for differences in country areas. Separate analyses were also conducted for mainland and island countries. All analyses clearly indicated the existence of latitudinal gradients. The most plausible explanation for the observed pattern is the so-called tropical conservatism hypothesis, which postulates (1) a tropical origin of many extant clades, (2) a longer time for cladogenesis in tropical environments thanks to their environmental stability, and (3) a limited ability of historically tropical lineages to adapt to temperate climates. Earwigs probably evolved on Gondwana and secondarily colonized the Northern Hemisphere. This colonization was hampered by both geographical and climatic factors. The Himalayan orogenesis obstructed earwig dispersal into the Palearctic region. Additionally, earwig preferences for warm/hot and humid climates hampered the colonization of temperate regions. Pleistocene glaciation further contributed to reducing diversity at northern latitudes.