A rapid rate of sex-chromosome turnover and non-random transitions in true frogs.

The canonical model of sex-chromosome evolution predicts that, as recombination is suppressed along sex chromosomes, gametologs will progressively differentiate, eventually becoming heteromorphic. However, there are numerous examples of homomorphic sex chromosomes across the tree of life. This homomorphy has been suggested to result from frequent sex-chromosome turnovers, yet we know little about which forces drive them. Here, we describe an extremely fast rate of turnover among 28 species of Ranidae. Transitions are not random, but converge on several chromosomes, potentially due to genes they harbour. Transitions also preserve the ancestral pattern of male heterogamety, in line with the 'hot-potato' model of sex-chromosome transitions, suggesting a key role for mutation-load accumulation in non-recombining genomic regions. The importance of mutation-load selection in frogs might result from the extreme heterochiasmy they exhibit, making frog sex chromosomes differentiate immediately from emergence and across their entire length

Protein requirement of tambaqui juveniles (Colossoma macropomum) after feed deprivation

The aim of this work was evaluate protein requirement of tambaqui (Colossoma macropomum) juveniles after feed deprivation. During 60 days, fish (50,3 ± 0,26 g) were fed on four isoenergetics diets with different protein content (28, 32, 36 and 40% crude protein) at two feeding regimes (with and without feed deprivation) under completely random factorial design (4x2) in triplicate. Water quality parameters and performance index were evaluated at 1º, 15º and 60º days. Water quality parameters were kept at normal fish cultivation patterns. No mortality in the tested treatments. There were observed differences among treatments for performance indexes analyzed: growth rate, feed efficiency, daily feed consumption, crude protein consumption, efficiency protein rate and relative weight gain, except for hepatosomatic index. Hyperfagia was detected indicating the occurrence of compensatory growth. Fat content and body protein deposition increased in fishes refed on 36% of crude protein. These results explain some data observed belong the experiment like the increase of weight gain, of the hyperfagia time extension, of the growth rate and of the feed efficiency. Therefore those fish shows increase on weight gain, hyperfagia time, growth rate and feed efficiency. There is no influence of feed deprivation on protein requirement tambaqui juveniles.O objetivo deste trabalho foi avaliar a exigência protéica de juvenis de tambaqui (Colossoma macropomum) após a privação alimentar. Os peixes (50,3 ± 0,26g) foram submetidos a quatro rações isoenergéticas com diferentes concentrações protéicas (28, 32, 36 e 40% proteína bruta) e dois regimes alimentares (com privação e sem privação) durante 60 dias. O delineamento experimental foi inteiramente casualizado, em esquema fatorial 4x2, em triplicata. Avaliaram-se os parâmetros de qualidade de água e de desempenho no 1º, 15º e 60º dia de experimento. Os parâmetros da qualidade da água permaneceram dentro dos padrões de cultivo. Não houve mortalidade nos tratamentos testados. Foram observados diferenças entre os tratamentos para os índices de desempenho analisadostaxa de crescimento específico, eficiência alimentar, consumo diário de ração, consumo de proteína bruta, taxa de eficiência protéica e ganho de peso relativo, com exceção do índice hepatossomático. Houve hiperfagia, indicando a existência de crescimento compensatório. Os peixes realimentados com 36% proteína bruta tiveram incremento no teor de gordura visceral e maior deposição de proteína corporal. Estes resultados explicam uma melhora nos dados de ganho de peso, duração da hiperfagia, taxa de crescimento e eficiência alimentar. A privação alimentar não influencia a exigência protéica em juvenis de tambaqui

Effect of stunting of juvenile bighead carp Aristichthys nobilis (Richardson) on compensatory growth and reproduction

The study was conducted to determine if stunting of young bighead carp Aristichtys nobilis (Richardson) would affect subsequent growth and reproduction. Juveniles (3 g each) were stocked directly in cages (control) in a lake or stunted in tanks for 6, 12, 18 or 24 months before being stocked in cages. Initially, body weights and lengths of stunted carp in cages were significantly lower (P0.05), but production was somewhat lower in fish stunted for 12 months

Identifying future research needs in landscape genetics: Where to from here?

Landscape genetics is an emerging interdisciplinary field that combines methods and concepts from population genetics, landscape ecology, and spatial statistics. The interest in landscape genetics is steadily increasing, and the field is evolving rapidly. We here outline four major challenges for future landscape genetic research that were identified during an international landscape genetics workshop. These challenges include (1) the identification of appropriate spatial and temporal scales; (2) current analytical limitations; (3) the expansion of the current focus in landscape genetics; and (4) interdisciplinary communication and education. Addressing these research challenges will greatly improve landscape genetic applications, and positively contribute to the future growth of this promising fiel

Desenvolvimento de tambaqui submetido a períodos de privação alimentar Growth of tambaqui submitted to different feed deprivation periods

O objetivo deste trabalho foi avaliar o efeito da privação alimentar em parâmetros de crescimento e composição corporal de juvenis de tambaqui (Colossoma macropomum). Em um delineamento inteiramente casualizado, 180 juvenis pesando 75,68&plusmn;8,62 g foram distribuídos em 12 tanques de 180 L e submetidos a quatro períodos de privação (0, 14, 21 e 28 dias). A massa média dos peixes ao final do período de privação alimentar foi menor à medida que o tempo de privação aumentou. Ao final do experimento, somente peixes submetidos a 14 dias de privação alcançaram a massa dos peixes alimentados sem restrição. O fator de condição não revelou diferenças significativas entre tratamentos ao final do período de privação ou ao final do experimento. As taxas de crescimento específico e o índice hepatossomático foram similares entre todos os tratamentos. Os peixes submetidos à privação exibiram os maiores valores de consumo diário de ração e os menores valores de eficiência alimentar. As porcentagens de umidade e proteína corporal foram maiores quanto maior o tempo de privação, mas não houve variações significativas dos níveis de extrato etéreo. Juvenis de tambaqui apresentam crescimento compensatório quando submetidos à privação alimentar.<br>The objective of this study was to evaluate the effect of feed deprivation on juvenile tambaqui (Colossoma macropomum) growth parameters and body composition. In a complete randomized design, one hundred and eighty fishes, weighting 75.68&plusmn;8.62 g were maintained in twelve 180-L tanks and submitted to four feed deprivation periods (0, 14, 21 and 28 days). Average fish weight at the end of feed deprivation period tended to be lower as deprivation period increased. At the end of the experiment only the fishes submitted to 14 days of feed deprivation attained similar weight to fish fed without restriction. Condition factor did not show any differences among treatments at the final of the deprivation period or at the end of the experiment. Specific growth rates and hepatosomatic index were similar among all treatments. Fish submitted to deprivation showed the highest daily feed consumption and lower feed efficiency values. Moisture and body protein contents were higher when feed deprivation increased but there was not a significant variation among ether extract levels. Tambaqui juveniles display compensatory growth when submitted to feed deprivation