Jean-François Agnèse

Effects of domestication on genetic variability, fertility, survival and growth rate in a tropical siluriform: Heterobranchus longifilis Valenciennes 1840

Abstract Fertility, survival rate, larval growth, as well as genetic variability at 23 loci, were analyzed in two populations representing the first and fourth generations of the African siluriform Heterobranchus longifilis Valenciennes (1840). A loss of genetic variability was observed in the fourth generation as compared to the first generation, and in the first generation as compared to the wild population studied earlier. Therefore, for 23 loci studied, only one single polymorphic locus with two alleles was observed for the fourth generation, two polymorphic loci with two alleles for the first generation. The first generation strain is characterized by a lower rate of deformed fry and greater survival to the 14th day compared to those of the fourth generation strain. This difference in the survival rate did not permit clear interpretation of the differences observed in growth rates. A study measuring the effect of stocking density on growth rate showed the negative correlation between stocking density and growth rate. These results show that H. longifilis is a species for which domestication may lead to loss of genetic variability and decreases in performance.

Fortes différences des ADN mitochonclriaux de populations de Sardinella aurita de la mer Méditerranée et de l'Atlantique Est

Digestion by restriction enzymes has been carried out on polymerase chain reaction products of the mitochondrial DNA control region of round sardine (Sardinella aurita) samples coming from the Eastern Atlantic and the Mediterranean Sea. The results show i) that, though the habitat is continuous, there is no gene flow between the two basins where two genetically differentiated groups can be recognized, ii) that each basin is genetically homogeneous and, iii) that the haplotypic diversity in the Mediterranean is between two and three times smaller than that observed in the Atlantic. These results can hardly be explained by a recent colonization from the Eastern Atlantic. This suggests that, for S. aurita and some other species, the Mediterranean Sea is genetically little influenced by the Eastern Atlantic.

Local Adaptation to Altitude Underlies Divergent Thermal Physiology in Tropical Killifishes of the Genus Aphyosemion

In watersheds of equatorial West Africa, monophyletic groups of killifish species (genus Aphyosemion) occur in discrete altitudinal ranges, low altitude species (LA, sea level to ∼350 m) or high altitude species (HA, 350 to 900 m). We investigated the hypothesis that local adaptation to altitude by the LA and HA species would be revealed as divergent effects of temperature on their physiological energetics. Two species from each group (mass ∼350 mg) were acclimated to 19, 25 and 28°C, with 19 and 28°C estimated to be outside the thermal envelope for LA or HA, respectively, in the wild. Wild-caught animals (F0 generation) were compared with animals raised in captivity at 25°C (F1 generation) to investigate the contribution of adaptation versus plasticity. Temperature significantly increased routine metabolic rate in all groups and generations. However, LA and HA species differed in the effects of temperature on their ability to process a meal. At 25°C, the specific dynamic action (SDA) response was completed within 8 h in all groups, but acclimation to temperatures beyond the thermal envelope caused profound declines in SDA performance. At 19°C, the LA required ∼14 h to complete the SDA, whereas the HA required only ∼7 h. The opposite effect was observed at 28°C. This effect was evident in both F0 and F1. Reaction norms for effects of temperature on SDA therefore revealed a trade-off, with superior performance at warmer temperatures by LA being associated with inferior performance at cooler temperatures, and vice-versa in HA. The data indicate that divergent physiological responses to temperature in the LA and HA species reflect local adaptation to the thermal regime in their habitat, and that local adaptation to one thermal environment trades off against performance in another.

A phylogeny of Cichlidogyrus spp. (Monogenea, Dactylogyridea) clarifies a host-switch between fish families and reveals an adaptive component to attachment organ morphology of this parasite genus

BackgroundParasite switches to new host species are of fundamental scientific interest and may be considered an important speciation mechanism. For numerous monogenean fish parasites, infecting different hosts is associated with morphological adaptations, in particular of the attachment organ (haptor). However, haptoral morphology in Cichlidogyrus spp. (Monogenea, Dactylogyridea), parasites of African cichlids, has been mainly linked to phylogenetic rather than to host constraints. Here we determined the position of Cichlidogyrus amieti, a parasite of species of Aphyosemion (Cyprinodontiformes, Nothobranchiidae) in the phylogeny of its congeners in order to infer its origin and assess the morphological changes associated with host-switching events.MethodsThe DNA of specimens of C. amieti isolated from Aphyosemion cameronense in Cameroon was sequenced and analyzed together with that of Cichlidogyrus spp. from cichlid hosts. In order to highlight the influence of the lateral transfer of C. amieti on the haptoral sclerotised parts we performed a Principal Component Analysis (PCA) to compare the attachment organ structure of C. amieti to that of congeners infecting cichlids.ResultsCichlidogyrus amieti was found to be nested within a strongly supported clade of species described from Hemichromis spp. (i.e. C. longicirrus and C. dracolemma). This clade is located at a derived position of the tree, suggesting that C. amieti transferred from cichlids to Cyprinodontiformes and not inversely. The morphological similarity between features of their copulatory organs suggested that C. amieti shares a recent ancestor with C. dracolemma. It also indicates that in this case, these organs do not seem subjected to strong divergent selection pressure. On the other hand, there are substantial differences in haptoral morphology between C. amieti and all of its closely related congeners described from Hemichromis spp..ConclusionsOur study provides new evidence supporting the hypothesis of the adaptive nature of haptor morphology. It demonstrates this adaptive component for the first time within Cichlidogyrus, the attachment organs of which were usually considered to be mainly phylogenetically constrained.

An important natural genetic resource of Oreochromis niloticus (Linnaeus, 1758) threatened by aquaculture activities in Loboi drainage, Kenya

The need to improve food security in Africa through culture of tilapias has led to transfer of different species from their natural ranges causing negative impacts on wild fish genetic resources. Loboi swamp in Kenya is fed by three hot springs: Lake Bogoria Hotel, Chelaba and Turtle Springs, hosting natural populations of Oreochromis niloticus. The present study aimed at better genetic characterization of these threatened populations. Partial mtDNA sequences of the D-loop region and variations at 16 microsatellite loci were assessed in the three hot spring populations and compared with three other natural populations of O. niloticus in the region. Results obtained indicated that the hot spring populations had mitochondrial and nuclear genetic variability similar to or higher than the large closely related populations. This may be attributed to the perennial nature of the hot springs, which do not depend on rainfall but rather receive permanent water supply from deep aquifers. The study also revealed that gene flow between the three different hot spring populations was sufficiently low thus allowing their differentiation. This differentiation was unexpected considering the very close proximity of the springs to each other. It is possible that the swamp creates a barrier to free movement of fish from one spring to the other thereby diminishing gene flow. Finally, the most surprising and worrying results were that the three hot spring populations are introgressed by mtDNA genes of O. leucostictus, while microsatellite analysis suggested that some nuclear genes may also have crossed the species barrier. It is very likely that the recent intensification of aquaculture activities in the Loboi drainage may be responsible for these introgressions. Taking into account the importance of these new genetic resources, protection and management actions of the Loboi swamp should be accorded top priority to prevent the loss of these spring populations.

Functional microsatellite and possible selective sweep in natural populations of the black-chinned tilapia Sarotherodon melanotheron (Teleostei, Cichlidae).

The Prolactin I (PrlI) gene is a key locus involved in fish osmotic regulation. Two microsatellites, PrlI GT and PrlI AC, are present in the promoter region of this gene in tilapias. One of these microsatellite is associated to PrlI gene expression and growth rate. Aquaria reared individuals homozygous for long microsatellite alleles at the PrlI AC locus expressed less PrlI in fresh water than fishes with other genotypes. To assess the occurrence of selection acting on these microsatellites we carried out a survey of their variability compared with four others microsatellites in natural populations. Samples of two tilapia species were studied, Oreochromis niloticus (6 samples) a typically freshwater species inhabiting osmotically stable environments and Sarotherodon melanotheron (5 samples) a brackish water species obliged and able to adapt very rapidly to any salinity changes. For both species the different populations studied exhibited a high amount of differentiation (all F(st) value were statistically significant) at every loci. Only one locus, PrlI AC, was monomorphic for the same allele in all S. melanotheron populations. We have hypothesized that this outlier locus with its unique allele could have experienced a selective sweep that took place in the early stages of the species origin. S. melanotheron represents an example of adaptation (to fluctuant salinity environment) acting indirectly on gene product through its promoter.

A comparative study of Ligophorus uruguayense and L. saladensis (Monogenea: Ancyrocephalidae) from Mugil liza (Teleostei: Mugilidae) in southern Brazil

Representatives of Ligophorus Euzet et Suriano, 1977 were found on the gills of Mugil liza Valenciennes caught in southern Brazil. They were identified as Ligophorus uruguayense Failla Siquier et Ostrowski de Núñez, 2009 and Ligophorus saladensis Marcotegui et Martorelli, 2009, even though specific identification proved to be difficult due to inconsistencies in some diagnostic features reported for these two species. Therefore, a combined morphological and molecular approach was used to critically review the validity of these species, by means of phase contrast and confocal fluorescence microscopical examination of sclerotised hard parts, and assessing the genetic divergence between L. saladensis, L. uruguayense and their congeners using rDNA sequences. The main morphological differences between the two species relate to the shape of the accessory piece of the penis and the median process of the ventral bar. The accessory piece in L. uruguayense is shorter than in L. saladensis, has a cylindrical, convex upper lobe and straight lower lobe (vs with the distal tip of the lower lobe turning away from the upper lobe in the latter species). The ventral bar has a V-shaped anterior median part in L. uruguayense (vs U-shaped in L. saladensis). The two species are suggested to be part of a species complex together with L. mediterraneus Sarabeev, Balbuena et Euzet, 2005. We recommend to generalise such comparative assessment of species of Ligophorus for a reliable picture of the diversity and diversification mechanisms within the genus, and to make full use of its potential as an additional marker for mullet taxonomy and systematics.

Morphological variations of wild populations of Nile tilapia (Oreochromis niloticus) living in extreme environmental conditions in the Kenyan Rift-Valley

In this study, we use geometric morphometric method to establish morphological differences between natural populations of Nile tilapia from two extreme environmental conditions (high temperature and salinity) in Kenya, and compare them to two populations from regions experiencing less extreme conditions. To determine genetic influence on morphology, we correlated genetic data with morphological data. The study observed significant morphological differences between all studied populations, including three closely related hot spring populations (Bogoria, Chelaba and Turtle Springs), and two populations with similar genetic background inhabiting saline environments in Lake Turkana basin (Turkana and Crocodile Lake populations). In addition, allometric growth patterns of the seven populations differed significantly, demonstrating that developmental changes (plastic or adaptive) operated between these populations. Positive correlation between morphometric and genetic data confirmed the influence of genetic factors on morphology. All observed differences were attributed either to genetic and/or environmental factors, which seemed to play a major role in influencing morphology of wild Nile tilapia populations. We recommend further studies to be carried out under controlled conditions to confirm the role of temperature, pH and salinity in morphological diversification of Nile tilapia.

A euryhaline fish, lost in the desert: The unexpected metapopulation structure of Coptodon guineensis (Günther, 1862) in the Sebkha of Imlili

Euryhaline Cichlid fish of the species Coptodon guineensis are present in different water holes situated in a dried depression in the desert in the extreme South of Morocco, the Sebkha of Imlili. A genetic survey of this population, using complete sequences of the ND2 gene (mtDNA) and sixteen microsatellite loci, revealed that the fish in the sebkha did not form a single population, but rather a metapopulation. This metapopulational structure may be regarded as good news from the point of view of the conservation of fish in the sebkha. Although small individual populations may have short, finite life spans, the metapopulation as a whole is more stable, because immigrants from one population are likely to re-colonize the habitat, left open by the extinction of another.

Physiological energetics may contribute to competitive exclusion in African killifish (Aphyosemion spp.).

In the equatorial watersheds of Cameroon, two monophyletic groups of killifish species (genus Aphyosemion) have a parapatric distribution based on altitude, one occupying altitudes to 400m (low altitude, LA) and the other altitudes above this (high altitude, HA). These groups are mutually exclusive although LA species occupy high altitudes in watersheds where HA species are absent. The basis for this apparent altitude-related competitive exclusion is unknown. This study investigated the hypothesis that LA and HA groups differ for the effects of temperature on their physiological energetics. Two species from each group (mass ~ 400 mg) were acclimated to 19°, 25° and 31 °C, and their appetite, metabolic rate (MR) and specific dynamic action response (SDA) compared. Appetite was assessed by feeding ad-libitum with live Artemia, MR and SDA by measuring patterns of instantaneous oxygen uptake. At 19 °C, there were no significant differences in appetite (~ 20% body mass after 72 h fast), or in routine MR (3.36 ± 0.47 vs 3.05 ± 0.38 mol O2 g -1 h-1 in HA vs LA, respectively, n = 12). When fed 5% of their body mass as Artemia, however, the HA species completed the SDA response faster than the LA (7.4 ± 1.1 vs 13.8 ± 0.8 h, respectively), with lower overall metabolic cost of the SDA (9.15 ± 1.88 vs 14.31 ± 1.92 kJ g-1, respectively). This is consistent with an energetic advantage to HA fish at 19°C. We are currently investigating effects at the other temperatures. Email Address for correspondence: david.mckenzie@univ-montp2.fr Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology Volume 153, Issue 2, Supplement 1, June 2009, Page S150 Abstracts of the Annual Main Meeting of the Society of Experimental Biology, 28th June 1st July, Glasgow, UK