Climatic fluctuations and orogenesis as motors for speciation in East Africa: case study on ParepistaurusKarsch, 1896 (Orthoptera)

Abstract

Mechanisms of speciation of flightless grasshoppers in mountainous and coastal East Africa are inferred considering (i) phylogenies estimated with a combination of molecular markers (16S rRNA locus, COI and H3), (ii) ecological data and (iii) the geographic distribution of Parepistaurus species. The study suggests that coastal taxa of Parepistaurus belong to ancestral lineages from which evolved the high diversity of species found in the Eastern Arc Mountains of Tanzania and Kenya, which are geologically ancient mountain formations. Network analyses and a molecular clock approach, calibrated with the geological age of the volcanoes, suggested that speciation was boosted by climatic fluctuations affecting large areas of East Africa. With the aridification beginning 2.8 Ma, forest taxa were isolated due to forest fragmentation and populations were separated by extended grasslands, which are avoided by Parepistaurus species. However, a humid period between 2.7 and 2.5 Ma triggered a spread of coastal taxa along the Eastern Arc Mountains. Forests expanded again and riparian vegetation along rivers draining into the Indian Ocean probably served as corridors for the dispersal of coastal taxa to the hinterland. The inland volcanoes such as Mount Kilimanjaro are therefore good time markers because their geological age is known, limiting the available time for speciation processes of mountainous Parepistaurus in the area to a maximum of about 1-2 Ma. A third humid but cold period between 1.1 and 0.9 Ma probably further boosted the spread of several flightless and montane-adapted Orthoptera taxa.

Africa’s highest mountain harbours Africa’s tallest trees

“…Submontane Newtonia forest relicts with 80-100 vascular plant species per 0.1 ha suggest a rich forest flora inhabited Kilimanjaro in former times, with undescribed or restricted-range species. The-compared with the Eastern Arc Mountains-observed low degree of endemism on Kilimanjaro may therefore result from the destruction of lower altitude forest rather than from the relatively young geologic age of the mountain (Hemp 2006b;Hemp et al 2015). The occurrence of the giant Entandrophragma adds another treasure to these valleys.…”

Ecology, acoustics and chromosomes of the East African genus Afroanthracites Hemp & Ingrisch (Orthoptera, Tettigoniidae, Conocephalinae, Agraeciini) with the description of new species

“…As seen in its morphology, species of adjacent areas seem to be most closely related suggesting that a spread of Afroanthracites is easily favoured when climatic conditions change to more humid conditions connecting forested areas. As shown in Hemp et al (2014) for the genus Parepistaurus climatic fluctuations of the past were the major drivers of speciation in the area. Evidence from lake sediments indicates humid periods for East Africa at 2.7-2.5, 1.9-1.7 and 1.1-0.9 Ma before present (Trauth et al 2005), the first two being humid and warm as supposed by Hemp et al (2014), the third one humid but cold.…”

“…As shown in Hemp et al (2014) for the genus Parepistaurus climatic fluctuations of the past were the major drivers of speciation in the area. Evidence from lake sediments indicates humid periods for East Africa at 2.7-2.5, 1.9-1.7 and 1.1-0.9 Ma before present (Trauth et al 2005), the first two being humid and warm as supposed by Hemp et al (2014), the third one humid but cold. While the first two humid and warm periods favoured the spread of lowland and submontane forest and with it its flora and fauna, driving montane forests to higher elevations, the third humid and cold period favoured a spread of montane taxa by creating corridors of montane vegetation.…”

Revision of the tropical African genus Tetraconcha (Orthoptera: Tettigoniidae: Phaneropterinae) with the description of ten new species

“…Climatic radiation is a type of geographic radiation in which allopatric speciation in the region is driven by changes in climate (Simões et al 2016). Speciation events are often correlated with humid and dry periods; forest expansion during humid periods and retraction during dry periods are considered the best explanation Journal of orthoptera research 2017, 26 (2) for the patterns of geographical species distribution found on East African mountains (Schultz et al 2007, Hemp et al 2015. Thus, following the above reported reconstruction, we may hypothesize that in the area of Dzanga-N'Doki tropical forest the ancestor of 'smaragdina-group' could have remained isolated in patches of forest during a dry period and derived populations could have met each other when the climate shifted to a warmer regime (African humid period).…”