Sesamia nonagrioides

Kergoat, Gael J., Toussaint, Emmanuel F. A., Capdevielle-Dulac, Claire, Clamens, Anne-Laure, Ong, George, Amo, Conlong, Desmond, Berg, Johnnie Van Den, Cugala, Domingos, Pallangyo, Beatrice, Mubenga, Onesime, Chipabika, Gilson, Ndemah, Rose, Sezonlin, Michel, Bani, Gregoire, Molo, Richard, Ali, Abdalla, Calatayud, Paul-Andre, Kaiser, Laure, Silvain, Jean-Francois & Ru, Bruno Le, 2015, Integrative taxonomy reveals six new species related to the Mediterranean corn stalk borer Sesamia nonagrioides (Lefèbvre) (Lepidoptera, Noctuidae, Sesamiina), Zoological Journal of the Linnean Society 175 (2), pp. 244-270 : 265

STRUCTURE OF S. NONAGRIOIDES

Both phylogenetic and population genetic analyses provided interesting new insights into the evolutionary history of S. nonagrioides . Dating analyses suggest that this species originated during the early Pleistocene about 1.81 Mya (95% HPD 1.28–2.57). We hypothesize that S. nonagrioides originated from Central Africa because the highest level of genetic diversity was found for Central African specimens, despite the fact that their number and the number of Central African localities sampled is consistently lower than those from East Africa. Another line of evidence to support this hypothesis is the fact that S. congoensis , the sister species of S. nonagrioides , is exclusively distributed in Central Africa. Finally, a Central African origin is also consistent with the evolutionary history and population structure of S. nonagrioides , with one lineage dispersing westward, and the other eastward ( Figs 1–3).

As already underlined in the study of Moyal et al. (2011c), the West African lineage appears to be genetically quite well differentiated from the remaining populations, despite the fact that geographical distances between the sampled localities in Benin (West Africa) and Cameroon (Central Africa) are less than those between the sampled localities in Cameroon and other Central African countries ( Democratic Republic of Congo, Republic of Congo and Zambia) ( Fig. 10). Overall, the West African lineage presents a very low proportion of shared haplotypes (none for the 16S, COI and Cytb fragments and only one for the 12S, 28S and EF1a fragments; Table S3). It is also found as sister to all other lineages under ML ( Fig. 1), with high BV support (87%). Finally, when estimating the mean genetic distance (COI, Kimura two-parameter dis- tance (K2P)) between specimens from West Africa and other individuals we recovered a value of 3.02%, which is compatible with expected distances between young species in Lepidoptera ( Hebert et al., 2003; Hajibabaei et al., 2006; Hebert, deWaard & Landry, 2010). However, this hypothesis is not backed up by morphological comparisons of specimens. Both West African populations and other populations also do not appear to have differences in terms of host plant range or ecology. Finally, PTP species delimitation analyses group West African specimens with individuals from other geographical areas in the same putative species cluster. It is worth highlighting that the pattern recovered for S. nonagrioides is remarkably similar to the phylogeographical pattern inferred for another sub- Saharan noctuid pest, Busseola fusca . In B. fusca most of the genetic differentiation was also found between populations from West Africa and populations from Central and East Africa ( Sezonlin et al., 2006; Dupas et al., 2014).

Regarding the Eastern lineage, a more complex phylogeographical pattern is recovered, with at least three East African populations and two East and Central African populations ( Fig. 3). Similar complex phylogeographical patterns have been reported in East Africa for mammals ( Lorenzen et al., 2012) and more recently for the maize stalk borer B. fusca ( Dupas et al., 2014) , suggesting the existence of a mosaic of refugia in the region. In fact, if the tectonic activity of this region fuelled a general aridification, it also engendered basins along the East African Rift Valley, probably to become large deep lakes during wet periods ( Trauth et al., 2010). This is supported by sedimentary records of East African lake deposits suggesting at least eight late Cenozoic lake periods between 4.6 Mya and the present ( Maslin et al., 2014). As currently recorded in many Rift Valley lakes (e.g. Turkana, Baringo, Bogoria, Elmenteita, Naivasha), lake shores are the most likely suitable habitats for S. nonagrioides host plants such as Cyperus spp. , Echinochloa spp. , Typha spp. and Vossia spp. At the same time, the great instability of these lakes could have contributed to the evolution of S. nonagrioides either by geographical isolation and/or shift to new host plant. These ephemeral lakes might have worked as a corridor facilitating the colonization of the Ethiopian region. Recent results obtained for B. fusca suggest that it may have achieved such dispersal ( Dupas et al., 2014).

The Eastern lineage also gave rise to the Palearctic lineage, whose origin is estimated at 0.178 Mya (95% HPD: 0.076 –0.306). For the latter our temporal framework is broadly consistent with the one inferred by Moyal et al. (2011c): in their study they relied on the standard evolution rate of 1.15% per Myr of Brower (1994) to estimate the origin of the Palearctic lineage at 0.108 Mya. Our results do not support their scenario of multiple independent colonizations of the Palearctic region and instead support the hypothesis of a unique colonization of the Palearctic region from East Africa. During the Late Pleistocene the Arabian Peninsula probably acted as a major biogeographical bridge between East Africa and the Palearctic region when shifts in climatic conditions increased moisture levels in this area ( Rosenberg et al., 2013). Our age estimate for the Palearctic lineage (0.178 Mya; 95% HPD: 0.076 –0.306) is highly congruent with one of the known Late Pleistocene humid periods (c. 0.2 Mya; Rosenberg et al., 2013) in the Arabian Peninsula. Partial support for this hypothesis is also provided by the results of the BI phylogenetic analysis ( Fig. 2) and the SplitsTree network ( Fig. 3), which connect the Palearctic lineage with an East African lineage from Ethiopia. An alternative scenario might be related to the present Nile river, which could have played a role as a corridor for the expansion of S. nonagrioides during a wet and hot period ( Moyal et al., 2011c).