River barriers and cryptic biodiversity in an evolutionary museum

Abstract

The Riverine Barriers Hypothesis (RBH) posits that tropical rivers can be effective barriers to gene flow, based on observations that range boundaries often coincide with river barriers. Over the last 160 years, the RBH has received attention from various perspectives, with a particular focus on vertebrates in the Amazon Basin. To our knowledge, no molecular assessment of the RBH has been conducted on birds in the Afrotropics, despite its rich avifauna and many Afrotropical bird species being widely distributed across numerous watersheds and basins. Here, we provide the first genetic evidence that an Afrotropical river has served as a barrier for birds and for their lice, based on four understory bird species collected from sites north and south of the Congo River. Our results indicate near-contemporaneous, Pleistocene lineage diversification across the Congo River in these species. Our results further indicate differing levels of genetic variation in bird lice; the extent of this variation appears linked to the life-history of both the host and the louse. Extensive cryptic diversity likely is being harbored in Afrotropical forests, in both understory birds and their lice. Therefore, these forests may not be “museums” of old lineages. Rather, substantial evolutionary diversification may have occurred in Afrotropical forests throughout the Pleistocene, supporting the Pleistocene Forest Refuge Hypothesis. Strong genetic variation in birds and their lice within a small part of the Congo Basin forest indicates that we may have grossly underestimated diversity in the Afrotropics, making these forests home of substantial biodiversity in need of conservation.

Isolation of peripheral populations of Canada lynx (Lynx canadensis)

“…Despite the number of empirical tests, support for this hypothesis is mixed (Colwell 2000). Rivers have been shown to impede dispersal and gene flow of a diversity of terrestrial species, including reptiles (lizards: Lamborot et al 2003), birds (Hayes and Sewlal 2004;Voelker et al 2013), and mammals (mustelids: Garroway et al 2011;primates: Ayres and Clutton-Brock 1992;Peres et al 1996). There are also examples of rivers that do not act as barriers (Patton et al 1994;Fairley et al 2002;Lougheed et al 1999;Côté et al 2012).…”

How did bonobos come to range south of the congo river? Reconsideration of the divergence of Pan paniscus from other Pan populations

“…84,85 In the same region, the phylogeographical analysis of forest understory specialist bird species indicates that a fording point appeared near 1 Ma. 86 Although geological evidence and paleogeographical studies are still limited, further phylogeographical studies may be useful in establishing the Congo River's history. red-tailed monkey (Cercopithecus ascanius), blue monkey (Cercopithecus mitis), and Angolian colobus (Colobus angolensis) are the common species occurring in the SC and EC areas.…”

Deep and wide valleys drive nested phylogeographic patterns across a montane bird community

“…However, species may respond differentially to topography and climate. Comparative phylogeographic analyses have thus far been conducted on subsets of bird communities; studies from the Americas [17][18][19], Africa [12,20,21], Australia [22] and southeast Asia [2] exhibit varied patterns among the species sampled. Such studies include species pairs that are often picked to make specific, often extreme, comparisons like wet/ humid species versus dry [17,23].…”