Androdioecy in Kryptolebias killifish and the evolution of self‐fertilizing hermaphroditism

Kryptolebias marmoratus is an important experimental fish, and is considered to represent the only vertebrate species comprising self‐fertilizing hermaphroditic individuals. Subsequent to the discovery of this unusual mode of reproduction, approximately 50 years ago, K. marmoratus has been the focus of a series of studies. However, little is known about the evolution of this rare reproduction mode, and data on the biology of closely related species are still unavailable. The present study aimed to histologically analyse the gonads of three K. marmoratus congeners (i.e. Kryptolebias ocellatus, Kryptolebias caudomarginatus, and Kryptolebias brasiliensis) to check the distribution of features related to hermaphroditism that are useful for forming hypotheses about the origin and evolution of the self‐fertilization mode of reproduction through the available phylogenies. The data obtained demonstrate that populations of K. caudomarginatus consist of males and hermaphrodites, which supports the hypothesis that hermaphroditism arose at the base of the clade containing K. caudomarginatus, K. marmoratus, and K. ocellatus as a first step towards a more advanced condition, uniquely shared by both K. marmoratus and K. ocellatus, in which males are rare or absent in natural populations, with the subsequent occurrence of self‐fertilization. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 344–349.     

Effect of diet on fatty acid compositions in Sciaenops ocellatus

The role of dietary polyunsaturated fatty acids (PUFAs) on the fatty acid composition of juvenile red drum Sciaenops ocellatus was investigated. Individuals (n = 435) were fed three natural diets (Gulf menhaden Brevoortia patronus, brown shrimp Farfantapenaeus aztecus and Atlantic brief squid Lolliguncula brevis) that had significantly different proximate composition, energy density and PUFA compositions for 40 days. Diets were characterized as containing: high lipid, high protein, high energy and low PUFA (fish‐based), low lipid, low protein, low energy, moderate PUFA (shrimp‐based), and low lipid, high protein, moderate energy and high PUFA levels (squid‐based), respectively. Specimens were collected at days 0, 5, 10, 20 and 40 to evaluate rate of dietary fatty acid composition in tissues. Two‐source mixing models were used to calculate dietary fatty acid accumulation in consumer tissues. Results indicated that juvenile red drum incorporated an average of 35% dietary PUFAs after 5 days. Although relative biomass and dietary proximate composition had an effect upon the dietary fatty acid contribution, red drum averaged 91% incorporation of the five most prevalent PUFAs [18 : 2 (n ? 6), 20 : 4 (n ? 6), 20 : 5 (n ? 3), 22 : 5 (n ? 3) and 22 : 6 (n ? 3)] across all diets after 40 days. Growth varied as a function of diet and rates were higher for individuals fed the squid diet than those fed shrimp or fish diets primarily due to increased levels of protein and PUFAs [including 22 : 6 (n ? 3); 25·8%] in the diet. Red drum fed squid exhibited the greatest increase in average dietary fatty acid contribution by day 5, a trend that continued for the duration of the experiment. Since PUFA composition in red drum was significantly influenced by diet in as few as 5 days and almost completely incorporated into body tissues after 40 days, results from this study support the premise that fatty acids (especially PUFAs) are promising dietary indicators and may be useful for future studies examining trophic relationships of estuarine and marine fishes.     

A trade-off generated by sexual conflict: Mediterranean wrasse males refuse present mates to increase future success

A variety of mechanisms, including intrasexual competition,intersexual conflict, and physiological constraints, can explainpatterns of reproduction and the adaptive value of specificbehaviors. In a Mediterranean wrasse, Symphodus ocellatus (Labridae),large, nesting males occasionally refuse to spawn with willingfemales in the presence of small, sneaker males. We exploredthe possible adaptive significance of this behavior. Nestingmales refuse females despite the fact that it reduces theirimmediate mating success. This nesting-male behavior also decreasesfemale and sneaker mating success and occurs when sneaker malessurround the nest. Experiments that decreased the number ofsneakers around nests showed that nesting males respond immediatelyto mating opportunities when fewer sneakers are present, andthus they are not simply constrained by a lack of energy orlack of sperm. Experiments that increased the number of sneakersat the nest caused nesting males initially to refuse spawningopportunities, followed by a subsequent decrease in sneakerpresence and an increase in mating rate. We propose that thisbehavior is the result of a trade-off between immediate matingsuccess and future reproduction created by competition betweenmales and conflict between the sexes. Males reduce their immediatemating success by reducing spawning at the nest; sneaker malessubsequently leave, and this decreases mate competition forthe nesting male. Unresponsiveness of nesting males also causessexual conflict between females and nesting males over mating.We argue that this behavior and the existence of a trade-offcan only be understood by examining intersexual conflict andintrasexual competition simultaneously.     

MATE CHOICE FOR NONADDITIVE GENETIC BENEFITS CORRELATE WITH MHC DISSIMILARITY IN THE ROSE BITTERLING (RHODEUS OCELLATUS)

Good genes models of mate choice predict additive genetic benefits of choice whereas the compatibility hypothesis predicts nonadditive fitness benefits. Here the Chinese rose bitterling, Rhodeus ocellatus, a freshwater fish with a resource‐based mating system, was used to separate additive and nonadditive genetic benefits of female mate choice. A sequential blocked mating design was used to test female mate preferences, and a cross‐classified breeding design coupled with in vitro fertilizations for fitness benefits of mate choice. In addition, the offspring produced by the pairing of preferred and nonpreferred males were reared to maturity and their fitness traits were compared. Finally, the MHC DAB1 gene was typed and male MHC genotypes were correlated with female mate choice. Females showed significant mate preferences but preferences were not congruent among females. There was a significant interaction of male and female genotype on offspring survival, rate of development, growth rate, and body size. No significant male additive effects on offspring fitness were observed. Female mate preferences corresponded with male genetic compatibility, which correlated with MHC dissimilarity. It is proposed that in the rose bitterling genetic compatibility is the mechanism by which females obtain a fitness benefit through mate choice and that male MHC dissimilarity, likely mediated by odor cues, indicates genetic compatibility.     

星丽鱼和天使鱼的核型及银染和C带

以肾细胞作材料,采用秋水仙素-低渗-空气干燥法、Howell的方法（银染）和Sumner的方法（C带）,制作染色体标本。报道了星丽鱼（Astronotus ocellatus）、天使鱼（Pterophyllum scalare）的核型及银染和C带。结果显示,这两种热带淡水观赏鱼的2n均为48。星丽鱼的核型公式为2n=2m＋26sm＋16st＋4t,NF=76,其染色体经快速银染后表明,在sm1的随体上出现银染位点;多数染色体的着丝点区均显示出一个深浅不同的C带,随体所在位置均深染。天使鱼具有异形性染色体,其核型公式为♀：2n=4m（X）＋12sm＋12st＋20t,NF=64;♂：2n=3m（x）＋12sm＋12st＋21t（Y）,NF=63。银染点位于sm3的短臂末端和X染色体的短臂末端;多数染色体为着丝粒C带。在两种鱼中均未见到Ag-NORs联合现象。