Population substructuring in the Utaka (TeleosteiPopulation substructuring in the Utaka (Teleostei, Cichlidae) from Lake Malawi (East Africa): do genetic and C c dae) o a e a a ( ast ca) do ge et c a d

(eco )morphological differentiation go hand in hand?(eco-)morphological differentiation go hand in hand?

Dieter Anseeuw graduated as Master in Engineering inPromotors:Land & Forest Management and obtained a degree of PhD

in Biology He studied the occurrence of non indigenous fishPromotors:Prof. Dr. Paul Busselen (KULeuven Campus Kortrijk)in Biology. He studied the occurrence of non-indigenous fish

species in Flanders and for his PhD study conducted

( p j )Prof. Dr. Jos Snoeks (KULeuven & Royal Museum of Central Africa)

Cspecies in Flanders and, for his PhD study, conductedgenetic and population biological research on East African

Co-promotors:Prof. Dr. Frans Ollevier (KULeuven)g p p g

cichlid fishes. He is the founder and co-organizer of theProf. Dr. Frans Ollevier (KULeuven)Dr. Erik Verheyen (Royal Belgian Institute of Natural Sciences)

annual West-Vlaamse Natuurstudiedag.

I t d tiIntroductionThe East African Great Lakes (Lakes Tanganyika Malawi and Victoria) are characterized by theThe East African Great Lakes (Lakes Tanganyika, Malawi and Victoria) are characterized by theinhabitance of an amazing number of fish species, 90% of them belonging to only one family, theinhabitance of an amazing number of fish species, 90% of them belonging to only one family, theCichlidae. Lake Malawi, in the southern part of the East African Rift Valley, harbours the worlds’ largestnumber of fishes (>800 species) found in a single lake. The vast majority consists of endemich l h i i hlid hi h h l d f t ithi th l t illihaplochromine cichlids, which have evolved from a common ancestor within the last million years.

Cichlid diversification and speciationCichlid diversification and speciationStudies of morphological and genetic variation of East African cichlidsStudies of morphological and genetic variation of East African cichlidssuggest that low dispersal capacities in combination with the patchygg p p p ydistribution of preferred habitats, differences in trophic biology, anddifferences in female mate choice preferences are the keymechanisms that have promoted the rapid diversification andmechanisms that have promoted the rapid diversification andspeciation in cichlidsspeciation in cichlids.

UtakaThe Utaka are a group of 30+ planktivorouscichlid species from Lake Malawi that arecichlid species from Lake Malawi that arecurrently classified in three genera:currently classified in three genera:Copadichromis, Mchenga andp gNyassachromis. Species are grouped into

fthe Utaka assemblage on the basis of theircharacteristic protractible mouth type Utakacharacteristic protractible mouth type. Utakatypically gather in schools to forage ontypically gather in schools to forage onpelagic zooplankton. Because of this Figure 1: Map showing Lake Malawi with the

behaviour, Utaka are intensively fished byl l fi h ith t i

g p gsampling locations where Utaka species (C.‘virginalis kajose’, C. quadrimaculatus, C.

local fishermen with open water seines. chrysonotus, C. borleyi and M. eucinostomus)were collected for this study.

ResultsResultsWe examined the phylogenetic position of the Utaka in the Malawi cichlid flock and detected theWe examined the phylogenetic position of the Utaka in the Malawi cichlid flock and detected thepresence of two distant and geographically widespread mtDNA lineages among the Utaka. Most ofp g g p y p g gUtaka specimens studied clustered with the non-Mbuna lineage. A second clade, mainly containing C.

‘ i i li k j ’ i i d b l DNA li W h h isp. ‘virginalis kajose’ specimens, constituted a separate basal mtDNA lineage (Figure 2). We hypothesizethat the latter originated through introgressive events involving a thus far unidentified (or extinct) nonthat the latter originated through introgressive events involving a thus far unidentified (or extinct) non-Utaka species.Utaka species.

Microsatellite variation among conspecific populations revealed that the studied Utaka species (theMicrosatellite variation among conspecific populations revealed that the studied Utaka species (thesand-dwelling C. sp. ‘virginalis kajose’ and M. eucinostomus, and the rock-dwelling C. quadrimaculatusg p g j , g qand C. chrysonotus) showed similar levels of genetic population substructuring. Habitat preference andgeographical barriers to dispersal appear to have only a limited effect on the degree of populationsubstructuring in contrast to many other demersal taxasubstructuring in contrast to many other demersal taxa.

Th i i t d h l i ll ll diff ti t d b t l l l d li t d t thThe species in our study are morphologically well differentiated, but are less clearly delineated at thegenetic level Within each species the populations showed only subtle genetic and morphological

Figure 2: mtDNA phylogeny of the Lake Malawicichlid flock Note that the Utaka specimens are genetic level. Within each species, the populations showed only subtle genetic and morphological

differentiation. The low level of genetic differentiation observed between and within species agrees withcichlid flock. Note that the Utaka specimens aredistributed over two distant lineages: the non-Mbuna clade and a separate ‘virginalis’ clade. g p g

the evolutionary young age of the Utaka and the potential persistence of shared ancestralbu a c ade a d a sepa ate g a s c ade

polymorphisms. We suggest that the distinct morphological differences observed between geneticallysimilar species are an indication for a rapid adapti e radiation i e speciation and a significant ecosimilar species are an indication for a rapid adaptive radiation, i.e. speciation and a significant eco-morphological differentiation that developed over a relatively short time spanmorphological differentiation that developed over a relatively short time span.

Further reading:Albertson et al. (1999). Phylogeny of a rapidly evolving clade: The cichlid fishes of Lake Malawi, East Africa. PNAS 96: 5107-5110.A t l (2008) S btl l ti t t d l bi d di l i t C di h i i (T l t i Ci hlid ) f L k M l i E t Af i H d bi l i 615 69 79Anseeuw et al. (2008). Subtle population structure and male-biased dispersal in two Copadichromis species (Teleostei, Cichlidae) from Lake Malawi, East Africa. Hydrobiologia 615: 69-79.Salzburger & Meyer (2004). The species flocks of East African cichlid fishes: recent advances in molecular phylogenetics and population genetics. Naturwissenschaften 91: 277-290.Snoeks (2004). The cichlid diversity of Lake Malawi/Nyasa/Niassa: Identification, distribution and taxonomy. Cichlid Press, El Paso, Texas: 360 pp.Snoeks (2004). The cichlid diversity of Lake Malawi/Nyasa/Niassa: Identification, distribution and taxonomy. Cichlid Press, El Paso, Texas: 360 pp.