The Ontogeny of Social Behavior and Body Coloration in the African Cichlid Fish Haplochromis burtoni

The ontogeny of behavioral patterns and body coloration are described for the African cichlid fish, Haplochromis burtoni. The development of particular color patterns correlates directly with appearance of behavioral patterns which “use” those color patterns. There is a flexible timetable associated with these events which depends on both social and environmental factors.     

Demography and genome divergence of lake and stream populations of an East African cichlid fish

Disentangling the processes and mechanisms underlying adaptive diversification is facilitated by the comparative study of replicate population pairs that have diverged along a similar environmental gradient. Such a setting is realized in a cichlid fish from southern Lake Tanganyika, Astatotilapia burtoni, which occurs within the lake proper as well as in various affluent rivers. Previously, we demonstrated that independent lake and stream populations show similar adaptations to the two habitat regimes. However, little is known about the evolutionary and demographic history of the A. burtoni populations in question and the patterns of genome divergence among them. Here, we apply restriction site‐associated DNA sequencing (RADseq) to examine the evolutionary history, the population structure and genomic differentiation of lake and stream populations in A. burtoni. A phylogenetic reconstruction based on genome‐wide molecular data largely resolved the evolutionary relationships among populations, allowing us to re‐evaluate the independence of replicate lake–stream population clusters. Further, we detected a strong pattern of isolation by distance, with baseline genomic divergence increasing with geographic distance and decreasing with the level of gene flow between lake and stream populations. Genome divergence patterns were heterogeneous and inconsistent among lake‐stream population clusters, which is explained by differences in divergence times, levels of gene flow and local selection regimes. In line with the latter, we only detected consistent outlier loci when the most divergent lake–stream population pair was excluded. Several of the thus identified candidate genes have inferred functions in immune and neuronal systems and show differences in gene expression between lake and stream populations.     

Growth of the teleost eye: novel solutions to complex constraints

Synopsis The cichlid fish, Haplochromis burtoni, is highly dependent on vision for survival in its natural habitat. As is true of most teleost fishes, the eyes continue to grow throughout life without any obvious changes in visual capability. In H. burtoni, for example, retinal area may increase by 27 × in just 6 months. During growth, there is no obvious change in the visual sensitivity, visual acuity or lens quality which must all be appropriate for the enlarging eye. This requires that during growth competing constraints be met. For example, to maintain visual acuity, the number of ganglion cells per visual angle subtended on the retina must remain the same as must the convergence ratio of the cones onto those ganglion cells. In contrast, to maintain visual sensitivity, the number of rod photoreceptors per unit retinal area must remain the same. These requirements are in conflict since a larger eye may preserve acuity with fewer cells per unit area in a larger retina. In addition, the lens properties must remain the same as the animal increases in size so that the image available is of similar quality throughout life. Experiments have been performed to reveal the adaptations during growth which allow the fish to preserve its image of the world throughout life.     

Field study of Haplochromis burtoni: Quantitative behavioural observations

Haplochromis burtoni observed in their natural habitat behave differently from those observed in aquaria in several respects. The majority of the territorial males observed in Lake Tanganyika living in a colony did not have the characteristic black eye bar as a part of their bright coloration, although otherwise the colour markings were identical. Those animals with eye bars appeared to be at a disadvantage in competition with barless fish for territories. The non-territorial males, females and juveniles are uniformly cryptically coloured and remained together in two or three large schools on the edge of the colony. These schools drifted slowly through the colony area, attempting to feed in the territories. Territorial males solicited females and chased non-territorial males. Sequences of behavioural events performed during courtship varied, depending on the local population density. Sound recordings showed no purposeful sounds associated with any behavioural acts.     

Effects of ship‐induced waves on littoral benthic invertebrates

1. Ship‐induced waves can affect the physical characteristics of lake and river shorelines, and laboratory studies have shown effects on littoral invertebrates. Here, we explored whether these effects could be observed under field conditions along a natural lake shore affected by wave sequences (trains) produced by boats. 2. Individuals of five invertebrate species (Bithynia tentaculata, Calopteryx splendens, Dikerogammarus villosus, Gammarus roeselii, Laccophilus hyalinus) were exposed to waves with increasing shear stress in five habitats differing in structural complexity. 3. Detachment of invertebrates increased with increasing shear stress and was best modelled using sigmoid response curves. Habitat structural complexity mitigated the effects of shear stress, and detachment rate was influenced more by habitat type than by species. A threshold (90% of the individual invertebrates unaffected) stress level of 0.64 N m^?2 was found for a structurally complex reed habitat, compared to 0.37 N m^?2 for a simple sand habitat. 4. Shear stress associated with wave trains created by recreational boating at a distance of 35 m from the shore and at a speed of 11 km h^?1 resulted in 45% detachment of littoral invertebrates. Decreasing the boat‐to‐shore distance to 20 m increased wave shear stress by 30% and invertebrate detachments up to 75%. 5. Disturbance of littoral habitats and invertebrate assemblages are widespread in inland waters used for recreational and/or commercial navigation. Our findings show that the integrity of littoral zones of navigable surface waters could be much improved by implementing management measures such as physically protecting complex habitats with dense reed belts and tree roots, and reducing boat speeds and increasing their minimum shoreline distance.     

Adaptive divergence between lake and stream populations of an East African cichlid fish

Divergent natural selection acting in different habitats may build up barriers to gene flow and initiate speciation. This speciation continuum can range from weak or no divergence to strong genetic differentiation between populations. Here, we focus on the early phases of adaptive divergence in the East African cichlid fish Astatotilapia burtoni, which occurs in both Lake Tanganyika (LT) and inflowing rivers. We first assessed the population structure and morphological differences in A. burtoni from southern LT. We then focused on four lake–stream systems and quantified body shape, ecologically relevant traits (gill raker and lower pharyngeal jaw) as well as stomach contents. Our study revealed the presence of several divergent lake–stream populations that rest at different stages of the speciation continuum, but show the same morphological and ecological trajectories along the lake–stream gradient. Lake fish have higher bodies, a more superior mouth position, longer gill rakers and more slender pharyngeal jaws, and they show a plant/algae and zooplankton‐biased diet, whereas stream fish feed more on snails, insects and plant seeds. A test for reproductive isolation between closely related lake and stream populations did not detect population‐assortative mating. Analyses of F1 offspring reared under common garden conditions indicate that the detected differences in body shape and gill raker length do not constitute pure plastic responses to different environmental conditions, but also have a genetic basis. Taken together, the A. burtoni lake–stream system constitutes a new model to study the factors that enhance and constrain progress towards speciation in cichlid fishes.     

The effect of social isolation on androgen and corticosteroid levels in a cichlid fish (Haplochromis burtoni) and in swordtails (Xiphophorus helleri)

The blood androgen and glucocorticoid levels of male Haplochromis burtoni and Xiphophorus helleri were measured in socially isolated individuals (8 and 4 weeks, respectively) and nonisolated controls. In both species social isolation leads to significant reductions of mean concentrations and variances, both for androgens and corticosteroids. It is known for H. burtoni—and new evidence for X. helleri is presented—that social isolation reduces aggressivity in nonescalating situations. It is proposed that social stimuli in both species stimulate the testes to produce more androgenic hormones, and that this can lead to higher levels of aggression. At least in tropical fish species the androgenic optimum for defending a territory or a social status may be much more controlled by social stimuli than previously realized.     

Olfactory responses to steroids in an African mouth-brooding cichlid, Haplochromis burtoni(Günther)

Underwater electro‐olfactogram (EOG) recordings involving 150 steroids and eight prostaglandins were used to determine which of these potential odorants are detected by the olfactory organ of an African cichlid, Haplochromis burtoni. In initial EOG tests at 10^?9 M, H. burtoni did not respond to unconjugated steroids or prostaglandins, but did respond to 17 conjugated steroids, 11 of which (17β‐oestradiol‐17β‐glucuronide; 17β‐oestradiol‐3‐sulphate; 17β‐oestradiol‐3,17β‐disulphate; epiandrosteron‐3β‐sulphate; etiocholanolone‐3α‐glucuronide; testosterone‐17β‐sulphate; dehydroepiandrosterone‐3β‐sulphate; 5α‐pregnan‐3β‐ol‐20‐one‐3β‐sulphate; 5β‐pregnan‐3α,17‐diol‐20‐one‐3α‐glucuronide; 5β‐pregnan‐3α,17,21‐triol‐11,20‐dione‐3α‐glucuronide; pregnenolone‐3β‐sulphate) were selected for EOG concentration‐response, cross‐adaptation and binary mixture tests. The EOG detection thresholds ranged from 10^?11 to 10^?9 M in all but one instance (female threshold to pregnenolone‐3β‐sulphate; 10^?8 M), and males and females exhibited only minor differences in EOG threshold or response magnitude. Results of EOG cross‐adaptation tests, which were supported by results of binary mixture tests, indicated that the response to the 11 steroid conjugates is mediated by five putative olfactory receptor mechanisms characterized by specificity for conjugate position and type: 3‐sulphate, 17‐sulphate, 3,17‐disulphate, 3‐glucuronide, 17‐glucuronide. Although there is no evidence that H. burtoni releases, or exhibits biological response to, the steroids shown to be detected in this study, the present results are suggestive of a complex pheromone system utilizing steroid conjugates.     

Use of three types of stream-margin habitat by age-0 brown trout late in the growing season

The use of stream-margin habitat by age-0 salmonids has been studied, but differences in use among various types of habitat along stream margins has not been addressed. We described the nighttime use of habitat features by age-0 brown trout (Salmo trutta) among three types of stream-margin habitat late in the growing season (August–September) and assessed the extent to which use of habitat features within each type differed over the sampling period. Differences in water depths, water velocities, distances from shore, and substrate at the locations of fish along the margins of pools, the margins of riffles, and in backwaters were studied. Variation in habitat use also was observed during the study period as fish increased in length. Our observations are important considerations when developing habitat suitability criteria for assessment of instream-flow needs of age-0 brown trout.     

Colonization of Sphagnum on land uplift islands in the Baltic Sea: time, area, distance and life history

Aim To test whether species richness of Sphagnum mosses on islands in a land uplift archipelago is related to island age, area or connectivity, and whether the frequency of different species can be predicted by their life history and autecology. Location The northern Stockholm archipelago in the Baltic Sea, east‐central Sweden, with a current land uplift rate of 4.4 mm year^?1. Methods We sampled 17 islands differing in area (0.55–55 ha), height (3.6–18 m, representing c. 800–4000 years of age) and distance from mainland (1.6–41 km). For each Sphagnum patch we measured area, height above sea level, horizontal distance from the shore and shading from vascular plants. Factors affecting island species richness, species frequency and habitats on the islands were tested by stepwise regressions. Species frequency was tested on nine life history and autecological variables, including estimated abundance and spore output on the mainland, habitat preference and distribution. Results We recorded 500 patches of 19 Sphagnum species, distributed in 83 rock pools on 14 islands. Island species richness correlated positively with island area and with degree of shelter by surrounding islands, while distance from the mainland, connectivity, height or age did not add to the model. Species frequency (number of colonized islands and rock pools) was mainly predicted by spore output on the mainland and by habitat preference (swamp forest species were more frequent than others), while spore size, for example, did not add to the model. Species differed in mean height above and horizontal distance from the shore, area of occupied rock pools and in the degree of shading of patches. The mean horizontal distance from the shore and the area of occupied rock pools correlated positively with the normal growth position above the water table among species. Spore capsules were found in only 2% of patches, mostly in the bisexual Sphagnum fimbriatum. Main conclusions The presence of Sphagnum in the Stockholm archipelago seems to be governed by regional spore production and habitat demands. Sphagnum does not appear to be dispersal limited at distances up to 40 km and time spans of centuries. Species with a high regional spore output have had a higher colonization rate, which, together with the rarity of spore capsules on the islands, indicate the mainland as a source for colonization rather than dispersal among islands. Swamp forest species seem more tolerant to the island conditions (summer droughts and some salt spray) than open mire species. The different distances from the sea occupied by the species indicate a slow, continuous succession and species replacement towards the island interior as islands are being uplifted and thus expand in area. This partly explains why larger islands harbour more species. Our results thus support some of the island biogeographical theories related to the species–area relationship.     

Species specificity and sexual dimorphism in tooth shape among the three sympatric haplochromine species in Lake Kivu cichlids

Tooth shape is used to differentiate between morphologically similar species of vertebrates, including fish. This study aimed to quantify tooth shape of three sympatric species: Haplochromis kamiranzovu, H. insidiae, and H. astatodon endemic to Lake Kivu, whose existing identification criteria are currently only qualitative. A quantitative tooth shape analysis was performed based on digitized tooth outline data with a subsequent elliptic Fourier analysis to test for differences among the three species. We looked at crown shape and size differences within H. kamiranzovu and H. insidiae at geographical, habitat, and gender levels. No comparison at habitat level was done for H. astatodon because it is found only in littoral zone. The analysis revealed significant tooth shape differences among the three species. Haplochromis astatodon had a significantly longer major cusp height and a longer and larger minor cusp than that of H. insidiae. It had also a longer major cusp height and a longer and larger minor cusp than that of H. kamiranzovu. Tooth shape differences of H. kamiranzovu and H. insidiae species were not significantly different between littoral and pelagic fish (p > .05) while differences were significant between southern and northern Lake Kivu populations (p < .05). Tooth sizes in H. kamiranzovu and H. insidiae were significantly different, both in height and width as well as in their ratios, and this was true at sex and geographic levels (p < .05), but not at habitat level (p > .05). Tooth shape was also significantly different with sharp teeth for males compared with females of southern populations versus northern ones. These shape‐ and size‐related differences between sexes suggest differences in the foraging strategies toward available food resources in the lake habitat. Further research should explain the genetic basis of the observed pattern.     

The human vocal cord surface

Summary The effect of phenylthiourea (PTU) on the pigment epithelium and the photoreceptor cells in the developing retina of Haplochromis burtoni was studied by electron microscopy. In the retinal pigment epithelium of 6-day old embryos, both types of melanin granule (spindle-shaped and rod-shaped) are already found. PTU inhibits the biosynthesis of melanin but does not influence the formation of premelanosomes so that in PTU-treated embryos there are no melanosomes, but an abundance of premelanosomes. The structure of the premelanosomes is described. It differs completely from that of all other vertebrates. Other changes: an increase in polysomes, retarded development of the inner segment of the photoreceptor cells and enlargement of the intercellular space between the inner and outer leaflet of the retina, may be due to a toxic effect of PTU.This investigation was supported by grants of the Deutsche Forschungsgemeinschaft     

Large-scale coexistence and small-scale segregation of key species on rocky shores

Biodiversity is defined by the scales at which organisms coexist. Coexistence at larger spatial scales may be underpinned by segregation at smaller spatial scales or temporal variability in behaviour and/or distribution. Limpets of the genus Patella are keystone grazers controlling the growth of macro-algae on many rocky shores. This study examined the distribution and abundance of P. vulgata and P. ulyssiponensis in relation to habitat and to each other at a range of spatial scales. Limpets were sampled on four shores on each of the east and west coasts of Ireland, in two different transects (10 m apart) at each of three shore heights in winter 2003 and summer 2004. P. vulgata and P. ulyssiponensis coexist around the coast of Ireland, but on shores where they co-occur, the pattern of coexistence begins to break down at the level of shore height: P. ulyssiponensis were more abundant on the low-shore than mid-shore, and P. vulgata were distributed evenly throughout the low and the mid-shore. At the level of habitat (pools vs. open rock), the two species exhibited a high degree of segregation: P. vulgata of all sizes were more common on open rock and P. ulyssiponensis of all sizes were more common in pools. The presence or absence of P. ulyssiponensis had no effect on the distribution of juvenile P. vulgata with respect to pools. Unexpectedly, however, a greater proportion of adult P. vulgata were found in pools at sites where P. ulyssiponensis were present in the pools than at sites where they were absent. The results of this study emphasize the need for multiple-scale analyses of the distribution and abundance of organisms to understand the organisation of natural assemblages. Handling editor: K. Martens     

Castration Lowers Aggression but not Social Dominance in Male Haplochromis burtoni (Cichlidae)

Adult males of the African cichlid fish Haplochromis burtoni are either territorial or nonterritorial. In nature and aquaria, only territorial males breed and they have markedly more developed testes than do nonterritorial males. Territorial males are clearly dominant over nonterritorial males of the same age and size, and also exhibit higher levels of aggression. In this study, territorial males were gonadectomized in order to assess the effects of lowered androgen levels on their aggression and dominance status. Completely castrated males showed a pronounced reduction in both testosterone and 11-ketotestosterone, as well as significantly lower aggression scores than sham-operated males. Partially castrated males (> 0.005 g gonadal tissue remaining at autopsy) exhibited intermediate levels of both androgen levels and aggression. Surprisingly, in dyadic encounters with normal nonterritorial males of the same size, castrated territorial males retained their dominance despite decreased androgen levels and aggression.     

Environmental conditions and phytoplankton in the Mwenda River,a small intermittent river flowing into Lake Kariba

Small intermittent rivers play an important role in the limnology of African lakes. The Mwenda River occurs on the southern shore of Lake Kariba. Its flow is governed by the incidence of tropical thunderstorms. During the dry period the river is reduced to a series of turbid pools. Physicochemically the river behaves similarly to a sheltered region of the lake. One river station deviates from the normal pattern because of the insulating effect of a Salvinia mat, and because of its permanent connection with the lake. River flooding flushes both nutrients and major ions into the lake. River phytoplankton populations peak prior to the flushing out of the river. Diatom populations are composed of cosmopolitan tropical taxa.     

The use of drinking sites, wallows and salt licks by herbivores in the flooded Middle Zambezi Valley

In the unflooded Middle Zambezi Valley, water was available for drinking in zoogenous pools in the deciduous woodlands of the escarpment hills only during, and for a short period after, the rains. For 5 or 6 months each year these pools were dry. During the dry season the majority of large mammals drank either from remnant pools in stream beds, or migrated to the Zambezi flood plain where water was available in the Zambezi River and in pools on the flood plain. In the part of the valley filled by Lake Kariba the Zambezi and its flood plain have been inundated, and the lake shore now lies permanently in the deciduous woodlands of the escarpment hills. Although the former riverine dry-season water sources have been removed, new sources are available along the lake shore. The suitability of the shore as a drinking site is affected by its exposure to wave action, its pitch, its soil type, and the vegetation type abutting on it, as well as by the preferences of the species using it. Elephant modify drinking sites on the shore by digging water-filled holes at the water's edge in clay soil, and elephant, buffalo and rhinoceros create wallows in similar situations. The holes dug by elephant are much used by antelope, especially impala, for drinking. By analogy with elephant-created pools in the woodlands, these zoogenous pools on the lake shore may have been a source of sodium for species drinking there. Such sources were not widely available in the dry season in the unflooded Zambezi Valley.     

Consistent patterns in diatom assemblages and diversity measures across water‐depth gradients from eight Boreal lakes from north‐western Ontario (Canada)

1. Until recently, the distribution of diatom species assemblages and their attributes (e.g. species richness and evenness) in relation to water depth have been identified but not quantified, especially across several lakes in a region. Here, we examined diatom assemblages in the surface sediment across a water‐depth gradient in eight small, boreal lakes in north‐western Ontario, minimally disturbed by human activities. 2. Surface‐sediment diatom assemblages were collected within each lake along a gentle slope from near‐shore to the centre deep basin of the lake, at a resolution of ～1 m water depth. Analysis of sedimentary samples provided an integrated view of assemblages that were living in the lake over several years and enabled a high‐resolution analysis of many lakes. The study lakes ranged in water chemistry, morphology and size and are located along an east–west transect approximately 250 km long in north‐western Ontario (Canada). 3. The majority of diatom species were distributed along a continuum of depth, with those taxa having similar habitat requirements forming distinct, though overlapping, assemblages. Three major zones of diatom assemblages in each lake were consistently identified: (i) a near‐shore assemblage of Achnanthes (sensu lato), Nitzschia, Cymbella (sensu lato) and other benthic species; (ii) a mid‐depth assemblage of small Fragilaria (sensu lato)/small Aulacoseira and various Navicula taxa; and (iii) a deep‐water assemblage of planktonic origin (mainly Discotella spp.). 4. The depth of the transition between assemblage zones varied between the eight lakes. The boundary between the deep‐water planktonic zone and the mid‐depth benthic zone varied according to water chemistry and was probably related to light attenuation. The boundary was deeper in lakes with the lower dissolved organic carbon and total phosphorus (TP) (i.e. less light attenuation) and vice versa. 5. Generally, species richness, species evenness and turnover rate of species as a function of depth were significantly lower in the planktonic assemblage zone in comparison with the two zones nearer the shore. Reproducibility of species and assemblage distributions across the depth gradient of the lakes illustrated that, despite potential for sediment transport, detailed ecological characterisation of diatom species can be gleaned from sedimentary data. Such data are often lacking, particularly for near‐shore benthic species.     

The puzzling phylogeography of the haplochromine cichlid fish Astatotilapia burtoni

Astatotilapia burtoni is a member of the “modern haplochromines,” the most species‐rich lineage within the family of cichlid fishes. Although the species has been in use as research model in various fields of research since almost seven decades, including developmental biology, neurobiology, genetics and genomics, and behavioral biology, little is known about its spatial distribution and phylogeography. Here, we examine the population structure and phylogeographic history of A. burtoni throughout its entire distribution range in the Lake Tanganyika basin. In addition, we include several A. burtoni laboratory strains to trace back their origin from wild populations. To this end, we reconstruct phylogenetic relationships based on sequences of the mitochondrial DNA (mtDNA) control region (d‐loop) as well as thousands of genomewide single nucleotide polymorphisms (SNPs) derived from restriction‐associated DNA sequencing. Our analyses reveal high population structure and deep divergence among several lineages, however, with discordant nuclear and mtDNA phylogenetic inferences. Whereas the SNP‐based phylogenetic hypothesis uncovers an unexpectedly deep split in A. burtoni, separating the populations in the southern part of the Lake Tanganyika basin from those in the northern part, analyses of the mtDNA control region suggest deep divergence between populations from the southwestern shoreline and populations from the northern and southeastern shorelines of Lake Tanganyika. This phylogeographic pattern and mitochondrial haplotype sharing between populations from the very North and the very South of Lake Tanganyika can only partly be explained by introgression linked to lake‐level fluctuations leading to past contact zones between otherwise isolated populations and large‐scale migration events.     

Gene expression remodelling and immune response during adaptive divergence in an African cichlid fish

Variation in gene expression contributes to ecological speciation by facilitating population persistence in novel environments. Likewise, immune responses can be of relevance in speciation driven by adaptation to different environments. Previous studies examining gene expression differences between recently diverged ecotypes have often relied on only one pair of populations, targeted the expression of only a subset of genes or used wild‐caught individuals. Here, we investigated the contribution of habitat‐specific parasites and symbionts and the underlying immunological abilities of ecotype hosts to adaptive divergence in lake–river population pairs of the cichlid fish Astatotilapia burtoni. To shed light on the role of phenotypic plasticity in adaptive divergence, we compared parasite and microbiota communities, immune response, and gene expression patterns of fish from natural habitats and a lake‐like pond set‐up. In all investigated population pairs, lake fish were more heavily parasitized than river fish, in terms of both parasite taxon composition and infection abundance. The innate immune response in the wild was higher in lake than in river populations and was elevated in a river population exposed to lake parasites in the pond set‐up. Environmental differences between lake and river habitat and their distinct parasite communities have shaped differential gene expression, involving genes functioning in osmoregulation and immune response. Most changes in gene expression between lake and river samples in the wild and in the pond set‐up were based on a plastic response. Finally, gene expression and bacterial communities of wild‐caught individuals and individuals acclimatized to lake‐like pond conditions showed shifts underlying adaptive phenotypic plasticity.     

Contrasting geographic structure in evolutionarily divergent Lake Tanganyika catfishes

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.