Hypoxia and male behaviour in an African cichlid Pseudocrenilabrus multicolor victoriae

This study tested the prediction that hypoxia may reduce the frequency of energetically expensive behaviours by quantifying male mating and aggressive displays in the cichlid Pseudocrenilabrus multicolor victoriae after long-term acclimation (5 months) to either high dissolved oxygen (DO) or low DO. Regardless of DO treatment, males engaged in more aggressive displays than mating displays; however, males acclimated to low DO reduced their total number of displays compared to high DO-acclimated males.     

The effect of hypoxia on sex hormones in an African cichlid Pseudocrenilabrus multicolor victoriae

Human activities increase the occurrence of aquatic hypoxia (low dissolved oxygen) globally. In fishes, short term hypoxia impairs multiple stages of reproduction (e.g., behavior, hormones, development), but no studies have investigated a species that lives and reproduces under hypoxia. This study examines the effects of hypoxia on sex hormones in the mouth brooding African cichlid Pseudocrenilabrus multicolor victoriae. Non-invasive measures of testosterone and estradiol levels in females were collected across the reproductive cycle in the laboratory, and at the time of capture in the field. In the laboratory, hormone levels were higher during pre-brooding (T=1.06, E2=1.62pg/mL/h) than brooding (T=0.61, E2=0.34pg/mL/h) or post-brooding (T=0.53, E2=0.51pg/mL/h) phases, but did not differ between hypoxic (1.2±0.0mg/L) and normoxic (7.3±0.1mg/L) populations. In the field, females were sampled from one low and one high oxygen population in two regions in Uganda (Mpanga River, Nabugabo Region). In both regions, hypoxic populations exhibited higher levels of testosterone than well-oxygenated populations, although there was no population level difference in estradiol levels. Hypoxic sites were also characterized by a higher testosterone/estradiol ratio and a lower proportion of brooding females. These results provide field evidence of hypoxia-mediated endocrine disruption in a fish species that experiences lifelong hypoxia.     

Fish embryo and juvenile size under hypoxia in the mouth-brooding African cichlid Pseudocrenilabrus multicolor

We used a field survey and a laboratory rearing experiment to (a) examine response (size and survival) to life-long hypoxia in offspring of the African maternal mouth-brooding cichlid Pseudocrenilabrus multicolor victoriae (Seegers) and (b) explore the degree to which developmental response can be environmentally-induced.Embryo size metrics were quantified in 9 field populations across a range of dissolved oxygen (DO) concentrations.In the laboratory,first generation (F1) broods of low-DO origin were reared under high or low DO.Brooding period was quantified for the mothers; and egg size,egg metabolic rate and juvenile size-at-release were quantified in their (F2) offspring.The F2 offspring were split and grown for 3 months post-release under high or low DO,and juvenile size and survival were quantified.In the field survey,across stages,embryos from low-DO field populations were shorter and weighed less than embryos from high-DO populations.In the laboratory experiment,F2 eggs and juveniles-at-release from mother's mouth did not differ in mass,length,survival regardless of development DO environment.However,juveniles diverged in size after leaving mother's mouth,exhibiting smaller size when grown under low DO.Size differences in embryo size across field populations and divergence in embryo size after release from the mother's mouthsupport predictions for smaller body size under hypoxia.There was no evidence for negative effects on survival of juveniles after 3 months.Brooding period was 16％ shorter in females reared under low DO suggesting that hypoxia may accelerate embryo development.This work provides insights into how bearer fishes respond to hypoxic stress relative to fishes with no post-spawning parental care; a shorter brooding interval and smaller body size may provide an optimal solution to parent and embryo survival under hypoxia in brooding fishes.     

As clear as mud: Turbidity induces behavioral changes in the African cichlid Pseudocrenilabrus multicolor

Aquatic biodiversity is being lost at an unprecedented rate.One factor driving this loss is increased turbidity,an environmental stressor that can impose behavioral,morphological,and/or physiological costs on fishes.Here we describe the behavioral response of a widespread African cichlid,Pseudocrenilabrus multicolor victoriae,to turbidity.We used a split-brood rearing design to test if F1 offspring reared in turbid water,originating from river (turbid) and swamp (clear) populations,behave differently than full-sibs reared in clear water.We examined two facets of behavior:(1) behaviors of fish in full sib groups,including activity level and social dynamics collected during the rearing period; and (2) male aggressive behavior directed at potential male competitors after fish had reached maturity; this was done in an experimental set-up independent of the rearing aquaria.Regardless of population of origin,fish reared in turbid water were marginally less active and performed fewer social behaviors than those reared in clear water.On the other hand,when tested against a competitor in turbid water,males performed more aggressive behaviors,regardless of population of origin or rearing environment.Our results suggest a plastic behavioral response to turbidity that may allow P multicolor to persist over a range of turbidity levels in nature by decreasing activity and general social behaviors and intensifying reproductive behaviors to ensure reproductive success [ Current Zoology 58 (1):146-157,2012].     

Isolation and characterization of tetranucleotide microsatellite markers in a mouth‐brooding haplochromine cichlid fish (Pseudocrenilabrus multicolor victoriae) from Uganda

Eight tetranucleotide microsatellite loci were isolated from the haplochromine cichlid fish, Pseudocrenilabrus multicolor victoriae, an important model species for studies in respiratory ecology, conservation, and evolution. We surveyed variation at these loci in 23 individuals from western Uganda, finding four to 19 alleles per locus and an average expected heterozygosity of 0.8575. These microsatellite loci will be used to examine gene flow and population structure in Ugandan P. m. victoriae.     

Respiratory oxygen consumption among groups of Pseudocrenilabrus multicolor victoriae subjected to different oxygen concentrations during development

The routine metabolic rate of Pseudocrenilabrus multicolor victoriae , laboratory-reared, F1 offspring of parents collected from a hypoxic swamp, did not differ between sibs raised under normoxia and hypoxia. In the offspring of parents originating from a river where the oxygen levels were generally high but fluctuating, the metabolic rate of fish raised under normoxia was higher than for sibs raised under extreme hypoxia. Although further experiments with a larger random sample of the parental stock will be necessary to validate the patterns, the difference between the experiments may indicate the selective environment of the parents.     

First report of metazoan parasites from the cichlid Pseudocrenilabrus philander and the cyprinid Enteromius paludinosus in a South African Ramsar wetland

Parasites of two small fish species from a Ramsar wetland in South Africa were studied in 2014–2015. The cichlid Pseudocrenilabrus philander (Weber, 1897) was parasitised by the copepod Lernaea cyprinacea Linnaeus, 1758, the monogenean Gyrodactylus thlapi Christison, Shinn & van As, 2005 and four gryporhynchid metacestode (Cyclophyllidea) species: Paradilepis scolecina (Rudolph, 1819), Paradilepis maleki Khalil, 1961, Neogryporhynchus lasiopeius Baer & Bona, 1960 and Valipora campylancristrota (Wedl, 1855). The cyprinid Enteromius paludinosus (syn. Barbus paludinosus) (Peters, 1852) was infected with the monogenean parasites Dogielius intorquens Crafford, Luus-Powell & Avenant-Oldewage, 2012, Dactylogyrus teresae Mashego, 1983, and three Dactylogyrus spp. These results represent several new locality as well as host records and further contribute information on the parasitic diversity in the Barberspan Ramsar wetland.     

Geographic variation in phenotypic plasticity in response to dissolved oxygen in an African cichlid fish

Genetic adaptation and phenotypic plasticity are two ways in which organisms can adapt to local environmental conditions. We examined genetic and plastic variation in gill and brain size among swamp (low oxygen; hypoxic) and river (normal oxygen; normoxic) populations of an African cichlid fish, Pseudocrenilabrus multicolor victoriae. Larger gills and smaller brains should be advantageous when oxygen is low, and we hypothesized that the relative contribution of local genetic adaptation vs. phenotypic plasticity should be related to potential for dispersal between environments (because of gene flow’s constraint on local genetic adaptation). We conducted a laboratory‐rearing experiment, with broods from multiple populations raised under high‐oxygen and low‐oxygen conditions. We found that most of the variation in gill size was because of plasticity. However, both plastic and genetic effects on brain mass were detected, as were genetic effects on brain mass plasticity. F₁ offspring from populations with the highest potential for dispersal between environments had characteristically smaller and more plastic brains. This phenotypic pattern might be adaptive in the face of gene flow, if smaller brains and increased plasticity confer higher average fitness across environment types.     

Male colour variation in a eurytopic African cichlid: the role of diet and hypoxia

Species that cross strong environmental gradients are expected to face divergent selective pressures that can act on sexually‐selected traits. In the present study, we examine the role of hypoxia and carotenoid availability in driving divergence in two sexually‐selected traits, male colour and reproductive behaviour, in the African cichlid Pseudocrenilabrus multicolor victoriae. Low‐dissolved oxygen (DO) (hypoxic) environments are expected to be energetically challenging; given that male nuptial colour expression and courtship displays can be costly, we expected fish in low‐DO versus high‐DO environments to differ in these traits. First, a field survey was used to describe natural variation in male nuptial colour patterns and diet across habitats divergent in DO. Next, using wild‐caught fish from a low‐DO and high‐DO habitat, we tested for differences in reproductive behaviour. Finally, a laboratory rearing experiment was used to quantify the interaction of DO and diet (low‐ versus high‐carotenoid availability) on the expression of male colour during development. In energetically challenging low‐DO environments, fish were more red and, in high‐DO environments, fish were typically brighter and more yellow. The frequency of reproductive displays in fish of low‐DO origin was 75% lower, although this had no consequence for brooding frequency (i.e. both populations produced the same number of broods on average). Our laboratory rearing study showed carotenoid availability to be important in colour production with no direct influence of DO on colour. Additionally, weak patterns of diet variation across wild populations suggest that other factors in combination with diet are contributing to colour divergence.     

The root of the East African cichlid radiations

Background  

For decades cichlid fishes (Perciformes: Cichlidae) of the East African cichlid radiations (Teleostei: Cichlidae) have served as natural experimental subjects for the study of speciation processes and the search for potential speciation key factors. Despite numerous phylogenetic studies dealing with their intragroup relationships, surprisingly little is known about the phylogenetic placement and time of origin of this enigmatic group. We used multilocus DNA-sequence data from five nuclear and four mitochondrial genes and refined divergence time estimates to fill this knowledge gap.     

Evolution of colour patterns in East African cichlid fish

African cichlid fishes have undergone outbursts of explosive speciation in several lakes, accompanied by rapid radiations in coloration and ecology. Little is known about the evolutionary forces that triggered these events but a hypothesis, published by Wallace Dominey in 1984, has figured prominently. It states that the evolution of colour patterns is driven by sexual selection and that these colour patterns are important in interspecific mate choice, a combination which holds the potential for rapid speciation. Here we present phylogenetic analyses that describe major events in colour evolution and test predictions yielded by Dominey's hypothesis. We assembled information on stripe patterns and the presence or absence of nuptial coloration from more than 700 cichlid species representing more than 90 taxa for which molecular phylogenetic hypotheses were available. We show that sexual selection is most likely the selection force that made male nuptial coloration arise and evolve quickly. In contrast, stripe patterns, though phylogenetically not conserved either, are constrained ecologically. The evolution of vertical bar patterns is associated with structurally complex habitats, such as rocky substrates or vegetation. The evolution of a horizontal stripe is associated with a piscivorous feeding mode. Horizontal stripes are also associated with shoaling behaviour. Strength of sexual selection, measured in terms of the mating system (weak in monogamous, strong in promiscuous species), has no detectable effects on stripe pattern evolution. In promiscuous species the frequency of difference between sister species in nuptial hue is higher than in pair bonding and harem forming species, but the frequency of difference in stripe pattern is lower. We argue that differences between the two components of coloration in their exposure to natural selection explain their very different evolutionary behaviour. Finally, we suggest that habitat-mediated selection upon chromomotor flexibility, a special form of phenotypic plasticity found in the river-dwelling outgroups of the lake-dwelling cichlids, explains the rapid and recurrent ecology-associated radiation of stripe patterns in lake environments, a new hypothesis that yields experimentally testable predictions.     

Determinants of variation in serum paraoxonase enzyme activity in baboons

Paraoxonase (PON), an HDL-associated enzyme, is one of many circulating antioxidants thought to play a vital protective role. To better understand the determinants of quantitative variation in serum PON activity, we assayed PON in samples from 611 pedigreed baboons fed three diets. PON was measured enzymatically; the main determinant of variation was genetic and consisted of at least three components: two loci detected by linkage analyses and a residual polygenic component. Multipoint linkage analyses gave peak log of the odds (LOD) scores on the baboon homolog of human chromosome 7q21-22 (near PON1, the structural gene) of 9.1 on the low-cholesterol, high-fat diet and 4.1 on the high-cholesterol, high-fat diet (genome-wide P values were 1 x 10(-8) and 0.0018, respectively). Surprisingly, a second locus on the baboon homolog of human chromosome 12q13 gave a LOD score of 2.9 on the high-cholesterol, high-fat diet (genome-wide P value was 0.032). We identified several significant covariates, including age, sex, diet, and apolipoprotein A-I concentrations. We estimate that 53% of total trait variation in baboons is explained by genes and 17% by covariates, thus accounting for approximately 70% of total variation in baboon PON. Although the generation of free radicals is influenced primarily by environmental factors, our findings suggest strong genetic regulation of one component in the antioxidant defense system that plays a major role in susceptibility to atherosclerosis.     

Alternative life-history styles of some African cichlid fishes

Synopsis About 50% of African cichlid species have been described. Little is known about cichlid ecology, behaviour or about the evolution and interactions of communities. Nevertheless, trends which provide an insight into cichlid life histories, into evolutionary alternatives and into behavioural alternatives which may be followed during the life time of these fishes are emerging. Cichlids which spend their entire life history in a single habitat belong to species flocks that have spectated greatly. In contrast, those groups which live in a variety of habitats during their life history have spectated little. Despite the trophic specializations that have occurred among cichlids, many and perhaps all species, have the ability to feed upon alternative food resources. They do so by switching or by markedly modifying their behaviour and all are particularly opportunistic. The extensive adaptive radiation of cichlids with regard to those attributes of morphology and behaviour that are associated with survival and growth, is apparently not matched by similar radiations in reproductive behaviour. The perceived evolutionary conservatism with regard to reproductive behaviour is attributed to the effects of stabilizing selection, but this still needs to be tested. The constraints of stabilizing selection appear to be lifted with regard to coloration. If colour is an important component of the specific-mate recognition system then it should also be subjected to stabilizing selection so the readiness with which colour variation occurs within and between populations needs explanation. Parental care in cichlids has followed a variety of evolutionary alternatives, all of which are geared to improve the chances of survival of offspring in their specific micro-habitats.     

Spectral sensitivity of the African cichlid fish,Haplochromis burtoni

Summary Spectral sensitivity of the cichlid fishHaplochromis burtoni was measured under both scotopic and photopic conditions using a two-choice, food reward, operant conditioning paradigm. The highest absolute sensitivity (scotopic) is one quantum for every 5 to 50 rods measured at 475 nm (equivalent to a corneal irradiance of 3.8×10⁶ Q s^–1 cm^–2). A P500₁ photopigment apparently mediates spectral sensitivity over most of the visible spectrum; microspectrophotometric studies of rods had previously shown them to contain this photopigment. However, the scotopic behavioral action spectrum shows a sensitivity to short wavelength light higher than is consistent with a P500₁ photopigment alone mediating the scotopic visual process. Determinations made under photopic conditions reveal a behavioral action spectrum broader than that found under scotopic conditions and consistent with mediation by interaction of the three known cone types in an opponent processing manner. The calculated photopic threshold value of approximately 10⁴ Q s^–1 (receptor)^–1 is in agreement with results from other species and corresponds to a corneal irradiance of about 7×10¹⁰Q s^–1cm^–2.     

Liver size reveals social status in the African cichlid Neolamprologus pulcher

Wild groups ( n = 167) of the cooperatively breeding Lake Tanganyika cichlid, Neolamprologus pulcher , were used to investigate how social status and sex influence liver investment. In contrast to expectations, males and females (controlling for body size) had similar liver investment and subordinates (both sexes) had relatively larger livers compared with dominants. Three hypotheses were considered for why social status results in liver size disparity: liver mass might reflect status-dependent differences in (1) energy expenditure, (2) energy storage and (3) energy acquisition. First, dominants performed more energetically costly behaviours ( e.g . social policing and care) compared with subordinates, supporting the notion that energy expenditure drives liver investment. Moreover, dominants in large groups (with many subordinates to monitor) and those holding multiple territories (with large areas to patrol), tended to have smaller livers. Second, subordinates did not appear to use the liver as a strategic energy storage organ. In laboratory and field experiments, subordinates ascending in rank had similar or larger livers during periods of rapid growth compared with non-ascending controls. Third, although subordinates fed more frequently than dominants, a negative relationship was found between feeding rates and liver size. Hence, these results contrast with previous liver studies and suggest that liver investment patterns were linked to status-driven differences in energy expenditure but not to energy intake or storage in N. pulcher .     

Natural hybrids of the African cichlid fishes Tilapia spilurus nigra and T. leucosticta: a case of hybrid introgression

Hybridization is documented between two species of African cichlid fishes, Tilapia spilurus nigra and T. leucosticta. First discovered in a rice padi at Tebere in eastern Kenya (ostensibly stocked only with T. s. nigra) , similar hybrids were later found in Lake Naivasha, Kenya (stocked inter alia with T. s. nigra and T. leucosticta). Hybrid characters are examined individually and by summation as a hybrid index. Pond and laboratory crosses indicate that hybridization occurs readily and produces at least partially fertile hybrids. Hybrid introgression appears to be occurring in the Tilapia populations of Lake Naivasha. Ecological features of the natural populations of both parental species and of the hybrids are examined with particular reference to habitat preferences and sex ratios.