Linking color polymorphism maintenance and speciation

Here, we review the recently burgeoning literature on color polymorphisms, seeking to integrate studies of the maintenance of genetic variation and the evolution of reproductive isolation. Our survey reveals that several mechanisms, some operating between populations and others within them, can contribute to both color polymorphism persistence and speciation. As expected, divergent selection clearly can couple with gene flow to maintain color polymorphism and mediate speciation. More surprisingly, recent evidence suggests that diverse forms of within-population sexual selection can generate negative frequency dependence and initiate reproductive isolation. These findings deserve additional study, particularly concerning the roles of heterogeneous visual environments and correlational selection. Finally, comparative studies and more comprehensive approaches are required to elucidate when color polymorphism evolves, persists, or leads to speciation.     

Modelling the maintenance of egg polymorphism in avian brood parasites and their hosts

In avian brood parasitism, egg phenotype plays a key role for both host and parasite reproduction. Several parrotbill species of the genus Paradoxornis are parasitized by the common cuckoo Cuculus canorus, and clear polymorphism in egg phenotype is observed. In this article, we develop a population genetics model in order to identify the key parameters that control the maintenance of egg polymorphism. The model analyses show that egg polymorphism can be maintained either statically as an equilibrium or dynamically with frequency oscillations depending on the sensitivity of the host against unlike eggs and how the parasite targets host nests with specific egg phenotypes. On the basis of the model, we discuss egg polymorphism observed in parrotbills and other host species parasitized by the cuckoo. We suggest the possibility that frequencies of egg phenotypes oscillate and we appeal for monitoring of cuckoo-host interactions over a large spatiotemporal scale.     

Predation and the maintenance of color polymorphism in a habitat specialist squamate

Multiple studies have addressed the mechanisms maintaining polymorphism within a population. However, several examples exist where species inhabiting diverse habitats exhibit local population-specific polymorphism. Numerous explanations have been proposed for the maintenance of geographic variation in color patterns. For example, spatial variation in patterns of selection or limited gene flow can cause entire populations to become fixed for a single morph, resulting in separate populations of the same species exhibiting separate and distinct color morphs. The mottled rock rattlesnake (Crotalus lepidus lepidus) is a montane species that exhibits among-population color polymorphism that correlates with substrate color. Habitat substrate in the eastern part of its range is composed primarily of light colored limestone and snakes have light dorsal coloration, whereas in the western region the substrate is primarily dark and snakes exhibit dark dorsal coloration. We hypothesized that predation on high contrast color and blotched patterns maintain these distinct color morphs. To test this we performed a predation experiment in the wild by deploying model snakes at 12 sites evenly distributed within each of the two regions where the different morphs are found. We employed a 2×2 factorial design that included two color and two blotched treatments. Our results showed that models contrasting with substrate coloration suffered significantly more avian attacks relative to models mimicking substrates. Predation attempts on blotched models were similar in each substrate type. These results support the hypothesis that color pattern is maintained by selective predation.     

Blood parasites of birds in Cameroon

Birds from south-central Cameroon, western Africa, were surveyed for blood parasites from August to October 1986. Of 331 birds examined, representing 65 species of 15 families and 6 orders (mostly passerines), 55 (17%) were found to be infected with 1 or more genera of hemotropic parasites. These included: Haemoproteus spp. (11% prevalence), Leucocytozoon spp. (3%), Plasmodium spp. (2%), Trypanosoma spp. (1%), and microfilariae of filariid nematodes (1%). Several new host-parasite associations were identified.     

The evolution, maintenance and adaptive function of genetic colour polymorphism in birds

The hypothesis that ornaments can honestly signal quality only if their expression is condition-dependent has dominated the study of the evolution and function of colour traits. Much less interest has been devoted to the adaptive function of colour traits for which the expression is not, or is to a low extent, sensitive to body condition and the environment in which individuals live. The aim of the present paper is to review the current theoretical and empirical knowledge of the evolution, maintenance and adaptive function of colour plumage traits for which the expression is mainly under genetic control. The finding that in many bird species the inheritance of colour morphs follows the laws of Mendel indicates that genetic colour polymorphism is frequent. Polymorphism may have evolved or be maintained because each colour morph facilitates the exploitation of alternative ecological niches as suggested by the observation that individuals are not randomly distributed among habitats with respect to coloration. Consistent with the hypothesis that different colour morphs are linked to alternative strategies is the finding that in a majority of species polymorphism is associated with reproductive parameters, and behavioural, life-history and physiological traits. Experimental studies showed that such covariations can have a genetic basis. These observations suggest that colour polymorphism has an adaptive function. Aviary and field experiments demonstrated that colour polymorphism is used as a criterion in mate-choice decisions and dominance interactions confirming the claim that conspecifics assess each other's colour morphs. The factors favouring the evolution and maintenance of genetic variation in coloration are reviewed, but empirical data are virtually lacking to assess their importance. Although current theory predicts that only condition-dependent traits can signal quality, the present review shows that genetically inherited morphs can reveal the same qualities. The study of genetic colour polymorphism will provide important and original insights on the adaptive function of conspicuous traits.     

Nematode parasites of birds of the fauna in Tunisia

330 birds of Tunisia were necropsied; they belong to 73 species among 29 families and 13 orders. We so collect 36 species of nematodes from 9 families. The relative importance of these is variable. The best represented are: Capillariidae (6 species), Spiruridae (6 species), Acuariidae (9 species) and Filariidae (6 species). The parasitism by nematodes is not uniform. Among the 330 birds autopsied only 51 were parasited by nematodes (15.45%) among 25 of the examined birds species (34.2%). Among these 25, sixteen (64%) presented only one species of parasitic nematode, six (24%) arboured two, (8%) three and only one, (partridges) presents six species of nematodes.     

The role of birds in the maintenance of tick-borne infections in the Tomsk anthropurgic foci

The role of birds in the focus of tick-borne infections was studied from 2006 to 2011. The frequency index of ticks carried by ground dwelling birds is about 49.7%. The index of their abundance is 3.8. The larvae of ticks have been found on birds in 43.8% of cases. Nymphs and adult ticks have been found in 39.9 and 16.3%, respectively. It was revealed that Ixodex pavlovskyi was transferred and dominated in the urban microfoci because of its ornithophily. The markers of infectious agents have been recorded in 42 of 60 bird species under study.     

A critical role for Neurofascin in regulating action potential initiation through maintenance of the axon initial segment

The axon initial segment (AIS) is critical for the initiation and propagation of action potentials. Assembly of the AIS requires interactions between scaffolding molecules and voltage-gated sodium channels, but the molecular mechanisms that stabilize the AIS are poorly understood. The neuronal isoform of Neurofascin, Nfasc186, clusters voltage-gated sodium channels at nodes of Ranvier in myelinated nerves: here, we investigate its role in AIS assembly and stabilization. Inactivation of the Nfasc gene in cerebellar Purkinje cells of adult mice causes rapid loss of Nfasc186 from the AIS but not from nodes of Ranvier. This causes AIS disintegration, impairment of motor learning and the abolition of the spontaneous tonic discharge typical of Purkinje cells. Nevertheless, action potentials with a modified waveform can still be evoked and basic motor abilities remain intact. We propose that Nfasc186 optimizes communication between mature neurons by anchoring the key elements of the adult AIS complex.     

Blood parasites in birds from Burkina Faso

This study aims at evaluating the prevalence and density of haemoparasites in a native population of immature and adult male and female birds of Burkina Faso. Protists from the orders Eucoccidiorida, Kinetoplastida, as well as microfilaria were found. During the period from the 27th to the 29th of November 2003, we trapped 110 birds: on 101 sampled birds, 47 harboured blood parasites, with an overall prevalence of infection of 46.5%; 15 birds (14.8%) harboured mixed infections. Haemoproteus (prevalence of infection 30.7%), Plasmodium (13.9%), Trypanosoma (10.9%), microfilaria (8.9%) and Leucocytozoon (5.9%) were most frequently recorded. Occurrence of blood parasites was very high in comparison to that seen in birds from other areas of Africa.     

A role for carnosine in cellular maintenance

The dipeptide L-carnosine has beneficial effects on cultured human fibroblasts. Physiological concentrations in standard media prolong their in vitro lifespan and strongly reduce the normal features of senescence. Late passage cells in normal medium are rejuvenated when transferred to medium containing carnosine, and become senescent when carnosine is removed. In the absence of pyruvate, carnosine is cytotoxic to neoplastic and transformed human and rodent cells. None of these effects are seen with its optical isomer, D-carnosine.     

The maintenance of sex in parasites

The maintenance of sex is an unresolved paradox in evolutionary biology, given the inherent twofold fitness advantage for asexuals. Parasitic helminths offer a unique opportunity to address this enigma. Parasites that can create novel antigenic strains are able to escape pre-existing host immunity. Viruses produce diversity through mutation with rapid clonal proliferation. The long generation times of helminth parasites prevent them from adopting this strategy. Instead, we argue that sexual reproduction enables parasitic helminths to rapidly generate strain diversity. We use both a stochastic, individual-based model and a simple analytical model to assess the selective value of sexual versus asexual reproduction in helminth parasites. We demonstrate that sexual reproduction can more easily produce and maintain strain diversity than asexual reproduction for long-lived parasites. We also show that sexual parasite populations are resistant to invasion by rare asexual mutants. These results are robust to high levels of cross-immunity between strains. We suggest that the enhancement of strain diversity, despite stochastic extinction of strains, may be critical to the evolutionary success of sex in long-lived parasites.     

Prevalence of blood parasites in European passeriform birds

Variation in the prevalence of blood parasites among species of birds has been used to test hypotheses about the effects of sexual selection and parental investment on disease resistance, and how vector abundance influences infection. However, the factors causing this variation are still poorly understood. We assessed the statistical effects of biogeographic, plumage-related and life-history traits on the prevalence of the blood parasites Plasmodium, Haemoproteus, Leucocytozoon and Trypanosoma in European passerine birds. Most of the variation in parasite prevalence occurred at low taxonomic levels. Brighter male plumage and greater host body mass were associated with higher prevalence, explaining 32% of the total variation. Male plumage brightness remained a significant factor when we controlled for phylogenetic effects. These relationships were driven primarily by simuliid-transmitted parasites (Leucocytozoon, Trypanosoma), which were more frequent in species with northern distributions. Host species with greater maximum longevity and shorter nestling periods had higher prevalences of Plasmodium; however, the effect was not stable after controlling for phylogeny using pairwise contrasts. Coevolution between hosts and parasites appears to create temporal and spatial variation that disconnects haematozoan prevalence from evolutionarily conservative life-history traits while creating some positive associations with traits that are phylogenetically labile. Clearly, ecologists should be cautious in relating patterns of variation in haematozoan prevalence to particular host traits.     

A role for antigen in the maintenance of immunological memory

The immune system has a memory that it exhibits in the enhanced and augmented responses the second time it meets an antigen. The memory is the result of a number of changes to the system brought about during the primary response. The most important of these changes is the formation of an expanded pool of antigen-specific memory cells. One of the enduring questions in immunology is how these memory cells are maintained for such long periods.     

Further observations on the blood parasites of birds in Uganda

Birds from three National Parks (Bwindi Impenetrable, Kibale, and Queen Elizabeth) in western Uganda were surveyed during the dry season in July 2003 and investigated for hematozoa by microscopic examination of stained blood films. Of 307 birds examined, representing 68 species of 15 families and four orders, 61.9% were found to be infected with blood parasites. Species of Haemoproteus (15.3% prevalence), Plasmodium (20.5%), Leucocytozoon (40.1%), Trypanosoma (11.4%), Hepatozoon (2.6%), Atoxoplasma (0.3%), and microfilariae (3.9%) were recorded. Except for Haemoproteus spp. infections, the overall prevalence of hematozoa belonging to all genera was significantly higher in this study than was previously reported in Uganda. Thirty-six species of birds were examined for blood parasites for the first time and 112 new host-parasite associations were identified. Eighty-one were at the generic and 31 at the specific level of the hematozoa. Hepatozoon and Atoxoplasma spp. were detected for the first time in Uganda.     

Blood parasites of some birds from Ghana

A total of 135 birds of 26 species in 13 families was examined for blood parasites; 43 birds (31.9%) of 13 species were infected; species of the Ploceidae were the most heavily infected. Species of Haemoproteus occurred most commonly 29 birds) while Leucocytozoon and Plasmodium species were virtually absent. There was no significant difference in the prevalence of hematozoa in birds from the mature rainforest and those in a savannah-urban setting.     

Blood parasites of some birds from Colombia

Blood films from 421 birds of 142 species, representing 29 avian families, from the environs of Cali, Colombia, were examined for blood parsites. Only 30 (7.1%) birds of 26 species harbored hematozoa. Species of Haemoproteus (3.1%) and microfilaria (2.3%) were the most commonly encountered blood parasites; species of Leucocytozoon, Plasmodium, Akiba and Lankesterella were found in a few birds. Mixed infections with more than one genus of blood parasite were rare; most infections encountered were of low intensity.     

Blood parasites of some birds from Senegal

A total of 809 birds from Senegal, including 43 species and 21 families, were examined for hematozoans; 93 birds (11.5%) harbored blood parasites, with only 7 (7.5%) harboring mixed infections. Species of Haemoproteus occurred in 81.7% of the infected birds while species of Plasmodium. Trypanosoma, microfilaria and Leucocytozoon were encountered less frequently. The majority of the sample was composed of species of ploceids and estrildidis and blood parasites were most prevalent in the colonial-nesting ploceids. Prevalence of blood parasites in Senegal was low in comparison to that seen in birds from other parts of Africa.     

A multifaceted role for ATM in genome maintenance

The pleiotropic nature of the clinical phenotypes of patients with ataxia-telangiectasia (A-T)--which encompass cerebellar degeneration (leading to ataxia), gonadal atrophy, and cancer predisposition--suggests multiple functions of the gene responsible for the disease. The ataxia-telangiectasia mutated gene product (ATM), whose loss of function is responsible for ataxia-telangiectasia, is a protein kinase that interacts with several substrates and is implicated in mitogenic signal transduction, chromosome condensation, meiotic recombination, cell-cycle control and telomere maintenance. This review focuses on the critical roles that ATM appears to play in cell-cycle checkpoints, DNA repair, telomere metabolism and oxidative stress, indicating how defects in these processes might lead to ataxia-telangiectasia.