Author:
Alter S. Elizabeth,Brown Bianca,Stiassny Melanie L. J.
Abstract
Abstract
Background
The lower Congo River (LCR) is a region of exceptional species diversity and endemism in the Congo basin, including numerous species of spiny eels (genus Mastacembelus). Four of these exhibit distinctive phenotypes characterized by greatly reduced optic globes deeply embedded into the head (cryptophthalmia) and reduced (or absent) melanin pigmentation, among other characteristics. A strikingly similar cryptophthalmic phenotype is also found in members of a number of unrelated fish families, strongly suggesting the possibility of convergent evolution. However, little is known about the evolutionary processes that shaped diversification in LCR Mastacembelus, their biogeographic origins, or when colonization of the LCR occurred.
Methods
We sequenced mitochondrial and nuclear genes from Mastacembelus species collected in the lower Congo River, and compared them with other African species and Asian representatives as outgroups. We analyzed the sequence data using Maximum Likelihood and Bayesian phylogenetic inference.
Results
Bayesian and Maximum Likelihood phylogenetic analyses, and Bayesian coalescent methods for species tree reconstruction, reveal that endemic LCR spiny eels derive from two independent origins, clearly demonstrating convergent evolution of the cryptophthalmic phenotype. Mastacembelus crassus, M. aviceps, and M. simbi form a clade, allied to species found in southern, eastern and central Africa. Unexpectedly, M. brichardi and brachyrhinus fall within a clade otherwise endemic to Lake Tanganikya (LT) ca. 1500 km east of the LCR. Divergence dating suggests the ages of these two clades of LCR endemics differ markedly. The age of the crassus group is estimated at ~4 Myr while colonization of the LCR by the brichardi-brachyrhinus progenitor was considerably more recent, dated at ~0.5 Myr.
Conclusions
The phylogenetic framework of spiny eels presented here, the first to include LCR species, demonstrates that cryptophthalmia and associated traits evolved at least twice in Mastacembelus: once in M. brichardi and at least once in the M. crassus clade. Timing of diversification is broadly consistent with the onset of modern high-energy flow conditions in the LCR and with previous studies of endemic cichlids. The close genetic relationship between M. brichardi and M. brachyrhinus is particularly notable given the extreme difference in phenotype between these species, and additional work is needed to better understand the evolutionary history of diversification in this clade. The findings presented here demonstrate strong, multi-trait convergence in LCR spiny eels, suggesting that extreme selective pressures have shaped numerous phenotypic attributes of the endemic species of this region.
Funder
PSC-CUNY
AMNH Axelrod Research Curatorship
Ms. Janine Luke
Publisher
Springer Science and Business Media LLC
Subject
Ecology, Evolution, Behavior and Systematics
Reference58 articles.
1. Winemiller KO, McIntyre PB, Castello L, Fluet-Chouinard E, Giarrizzo T, Nam S, et al. Hydropower expansion in the Amazon, Congo and Mekong - a looming threat to global biodiversity. Science. In revision.
2. Stiassny M, Brummett R, Harrison I, Monsembula R, Mamonekene V. The status and distribution of the freshwater fishes of Central Africa. In: Darwall W, Smith K, Allen D, Holland R, Harrison I, Brooks E, editors. The diversity of life in African freshwaters: underwater, under threat An analysis of the status and distribution of freshwater species throughout mainland Africa, vol. IUCN Red List of Threatened Species, Regional Assessment. Gland: IUCN; 2011. p. 27–46.
3. Lowenstein JH, Osmundson TW, Becker S, Hanner R, Stiassny ML. Incorporating DNA barcodes into a multi-year inventory of the fishes of the hyperdiverse Lower Congo River, with a multi-gene performance assessment of the genus Labeo as a case study. Mitochondrial DNA. 2011;22(sup1):52–70.
4. Vreven EJ, Stiassny ML. Mastacembelus simbi, a new dwarf spiny eel (Synbranchiformes: Mastacembelidae) from the lower Congo River. Ichthyological Exploration of Freshwaters. 2009;20(3):213.
5. Grant PR, Grant BR, Markert JA, Keller LF, Petren K. Convergent evolution of Darwin’s finches caused by introgressive hybridization and selection. Evolution. 2004;58(7):1588–99.
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