On the origin of the Synodontis catfish species flock from Lake Tanganyika.
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ABSTRACT:
SUBMITTER: Day JJ
PROVIDER: S-EPMC1833983 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The polytypic Nicaraguan Midas cichlids (Amphilophus cf. citrinellus) have been established as a model system for studying the mechanisms of speciation and patterns of diversification in allopatry and sympatry. The species assemblage in Crater Lake Apoyo has been accepted as a textbook example for sympatric speciation. Here, we present a first comprehensive data set of population genetic (mtDNA & AFLPs) proxies of species level differentiation for a representative set of individuals of all six endemic Amphilophus species occurring in Crater Lake Apoyo. AFLP genetic differentiation was partitioned into a neutral and non-neutral component based on outlier-loci detection approaches, and patterns of species divergence were explored with Bayesian clustering methods. Substantial levels of admixture between species were detected, indicating different levels of reproductive isolation between the six species. Analysis of neutral genetic variation revealed several A. zaliosus as being introgressed by an unknown contributor, hereby rendering the sympatrically evolving L. Apoyo flock polyphyletic. This is contrasted by the mtDNA analysis delivering a clear monophyly signal with Crater Lake Apoyo private haplotypes characterising all six described species, but also demonstrating different demographic histories as inferred from pairwise mismatch distributions.
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Project description:Background:Species delineation is particularly challenging in taxa with substantial intra-specific variation. In systematic studies of fishes, meristics and linear measurements that describe shape are often used to delineate species. Yet, little is known about the taxonomic value of these two types of morphological characteristics. Here, we used Tropheus (Teleostei, Cichlidae) from the southern subbasin of Lake Tanganyika to test which of these types of characters best matched genetic lineages that could represent species in this group of stenotypic rock-dwelling cichlids. We further investigated intra-population variation in morphology. By linking this to a proxy of a population's age, we could assess the evolutionary stability of different kinds of morphological markers. Results:Morphological data was collected from 570 specimens originating from 86 localities. An AFLP approach revealed the presence of five lineages in the southern subbasin: T. moorii, T. brichardi, T. sp. 'maculatus', T. sp. 'Mpimbwe' and T. sp. 'red', which we consider to represent distinct species. Although both types of morphological data supported this classification, a comparison of PST-values that describe inter-population morphological differentiation, revealed a better correspondence between the taxon delineation based on AFLP data and the patterns revealed by an analysis of meristics than between the AFLP-based taxon delineation and the patterns revealed by an analysis of shape. However, classifying southern populations of Tropheus was inherently difficult as they contained a large amount of clinal variation, both in genetic and in morphological data, and both within and among species. A scenario is put forward to explain the current-day distribution of the species and colour varieties and the observed clinal variation across the subbasin's shoreline. Additionally, we observed that variation in shape was larger in populations from shallow shores whereas populations from steep shores were more variable in meristics. This difference is explained in terms of the different timescales at which small and large scale lake level fluctuations affected populations of littoral cichlids at steep and shallow shores. Conclusions:Our results showed meristics to be more evolutionary stable, and of higher taxonomic value for species delimitation in Tropheus, than linear measurements that describe shape. These results should be taken into account when interpreting morphological differences between populations of highly stenotypic species, such as littoral cichlids from the Great East African Lakes.
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Project description:Geographic isolation is suggested to be among the most important processes in the generation of cichlid fish diversity in East Africa's Great Lakes, both through isolation by distance and fluctuating connectivity caused by changing lake levels. However, even broad scale phylogeographic patterns are currently unknown in many non-cichlid littoral taxa from these systems. To begin to address this, we generated restriction-site-associated DNA sequence (RADseq) data to investigate phylogeographic structure throughout Lake Tanganyika (LT) in two broadly sympatric rocky shore catfish species from independent evolutionary radiations with differing behaviors: the mouthbrooding claroteine, Lophiobagrus cyclurus, and the brood-parasite mochokid, Synodontis multipunctatus. Our results indicated contrasting patterns between these species, with strong lake-wide phylogeographic signal in L. cyclurus including a deep divergence between the northern and southern lake basins. Further structuring of these populations was observed across a heterogeneous habitat over much smaller distances. Strong population growth was observed in L. cyclurus sampled from shallow shorelines, suggesting population growth associated with the colonization of new habitats following lake-level rises. Conversely, S. multipunctatus, which occupies a broader depth range, showed little phylogeographic structure and lower rates of population growth. Our findings suggest that isolation by distance and/or habitat barriers may play a role in the divergence of non-cichlid fishes in LT, but this effect varies by species.
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Project description:Functional coupling, where a single morphological trait performs multiple functions, is a universal feature of organismal design. Theory suggests that functional coupling may constrain the rate of phenotypic evolution, yet empirical tests of this hypothesis are rare. In fish, the evolutionary transition from guarding the eggs on a sandy/rocky substrate (i.e. substrate guarding) to mouthbrooding introduces a novel function to the craniofacial system and offers an ideal opportunity to test the functional coupling hypothesis. Using a combination of geometric morphometrics and a recently developed phylogenetic comparative method, we found that head morphology evolution was 43% faster in substrate guarding species than in mouthbrooding species. Furthermore, for species in which females were solely responsible for mouthbrooding the males had a higher rate of head morphology evolution than in those with bi-parental mouthbrooding. Our results support the hypothesis that adaptations resulting in functional coupling constrain phenotypic evolution.
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Project description:BackgroundMalaria is among the most common causes of death along Lake Tanganyika, a problem which many aid organizations have attempted to combat through the distribution of free mosquito bed nets to high-risk communities. The Lake Tanganyika Floating Health Clinic (LTFHC), a health-based non-governmental organization (NGO), has observed residents of the Lake Tanganyika basin using bed nets to fish small fry near the shoreline, despite a series of laws that prohibit bed net use and other fine-gauge nets for fishing, implemented to protect the near-shore fish ecology. The LTFHC sought to quantify the sources of bed nets and whether they were being used for fishing.MethodsThe LTFHC conducted a survey of seven lakeside villages in Lagosa Ward, Tanzania. The government has divided each village into two to six pre-existing geographic sub-villages depending on population size. Seven households per sub-village were chosen at random for survey administration. The survey consisted of 23 questions regarding mosquito bed net practices, including the use of bed nets for fishing, as well as questions pertaining to any perceived changes to the fish supply.ResultsA total of 196 surveys were administered over a four-week period with a 100% response rate. Over 87% of households surveyed have used a mosquito bed net for fishing at some point. The majority of respondents reported receiving their bed net for free (96.4%), observing "many" residents of their village using bed nets for fishing (97.4%), and noticing a subjective decrease in the fish supply over time (64.9%).ConclusionsThe findings of this study raise concerns that the use of free malaria bed nets for fishing is widespread along Lake Tanganyika, and that this dynamic will have an adverse effect on fish ecology. Further studies are indicated to fully define the scope of bed net misuse and the effects of alternative vector control strategies in water-based communities.
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