Selection of sites for egg deposition and spawning dynamics in the waccamaw darter

Synopsis We provided 93 experimental spawning covers for the waccamaw darter. We grouped the covers (3 sizes of slate and one of concave tile) in three arrangements at six Lake Waccamaw locations to separate the variables of water depth, distance from shore, cover density and cover type. Tag returns of marked males suggest low fidelity for nest sites. Egg production under the 3 different sizes of slate was not significantly different. Egg production under the tile was significantly less than that under the slates. Egg production was significantly higher off the undeveloped southeastern shore in 2 m of water and lowest at the shallowest location with the highest experimental cover density. The number of eggs in nest is positively correlated with male size. We conclude that medium size slate covers placed in a linear arrangement in 2 m of water on a mixed sand bottom result in the highest egg production for the waccamaw darter.     

大鳞裂峡鲃繁殖生物学特征

2009、2010和2013年在云南省西双版纳自治州勐腊县境内的南腊河共收集大鳞裂峡鲃(Hampala macrolepidota)样本438尾。研究结果表明:大鳞裂峡鲃雌性群体初次性成熟体长228 mm、体重270.3 g,雄性群体初次性成熟体长205 mm、体重172.5 g,对应年龄均为4龄。大鳞裂峡鲃雌、雄繁殖群体的成熟系数年度变化趋势基本一致。成熟系数值在1月、3月、4月呈逐渐增大趋势,5月显著上升,6月达到最高峰,7月急速下降,8月至9月趋于平缓。繁殖活动每年4月开始,一直可持续至10月,主要集中在5~6月。大鳞裂峡鲃雌雄性比为1︰1.19,与鲃亚科其他部分鱼类雌性数量多于雄性的情况相反;繁殖盛期则雌性数量多于雄性。繁殖群体由4~8龄共5个年龄组组成,雌、雄群体均以5龄组所占比例最大。大鳞裂峡鲃属单次产卵鱼类。平均卵径1.18 mm;绝对繁殖力为63 393粒,相对繁殖力为70.04粒/g。与鲃亚科其他部分鱼类比较,大鳞裂峡鲃的卵径相对较小而繁殖力较大。     

Mating system in the tarantula spider Eupalaestrus weijenberghi (Thorell, 1894): evidences of monandry and polygyny

The road tarantula Eupalaestrus weijenberghi shows a strongly female-biased sex ratio since adult females live several years while adult males live only for 2 months. In this scenario selective males could be expected. However, several factors such as the rates of reproduction of each sex, degree of sexual selectivity and synchronicity of female receptiveness determine the operational sexual ratio and mating system of the species. Our objective was to determine the mating rates and mating tactics for females and males of E. weijenberghi and their variation throughout the reproductive period. Four hundred sexual encounters among 20 females and 20 males in all possible pair-wise combinations were carried out during 29 days, a brief but intense experimental period, as it also occurs in the field. Mating success differed strongly between sexes. Females mated once: five females mated at the first attempt, eight initially rejected males and copulated in subsequent attempts. Half of the males did not copulate and the others copulated 1-3 times. Mated females actively rejected males. Results indicate a mating system with monogamous females and polygamous males. Not all the females were receptive in every reproductive season. We suggest that female monogamy drastically affects the operational sex ratio, since several females were unreceptive after a single copulation, directly diminishing the male potential reproductive rate. This is the first experimental approach to estimate tarantula mating systems, their determinants and the consequences of the strategies shown by each sex.     

Spawning behavior of the pygmy leatherjacket Brachaluteres jacksonianus (Monacanthidae) in southeastern Australia

Spawning behavior of the pygmy leatherjacket Brachaluteres jacksonianus was studied in southeastern Australia. Prespawning females thrust the snout repeatedly into spawning substrata, while males exhibited courtship display and nuzzled the female’s face. The females and males touched their abdomens in pairs and released gametes. No parental egg care was observed after spawning. Fertilized eggs measured 0.74 mm in diameter, and each clutch contained 50–191 eggs. The eggs were attached to filamentous red algae, which were found on the surface of the seagrass and other substrata. Reproductive ecology of B. jacksonianus is similar to that of congeneric Brachaluteres ulvarum, although selection of spawning substrata differed in two species.Supplementary material to this paper is available in electronic format at http://dx.doi.org/10.1007/s10228-005-0272-8     

Reproductive biology of Tilapia zillii (Gervais) in Lake Naivasha,Kenya

Synopsis Tilapia zillii breeds all year round in the equatorial Lake Naivasha with slightly high breeding intensity during wet months (March, May and July–August). A sex ratio of 1 : 1.28 was found between males and females. The smallest mature male and female were 9.0 and 11.0 cm respectively. The fecundity ranged from 2990 to 12344 eggs, with a mean of 6606 eggs. Fecundity showed a curvilinear relationship with total length (log F = 1.7034 + 1.6370 log L) and a linear relationship with body weight (F = 2197 + 28.76 W)     

Sexual size dimorphism,growth, and maturity of the fluvial eight-barbel loach in the Kako River,Japan

The maturation and growth pattern of the fluvial eight-barbel loach Lefua sp. (Japanese name: nagare-hotoke-dojo), an endangered species, was investigated using an individual identification-recapture method from 1995 to 1998 in an upper reach of a headwater tributary of the Kako River, Hyogo Prefecture, Japan. Based on observations of the gonads through the abdominal skin, the loach was estimated to breed mostly from May to July. All the males matured by age 1⁺, and all the females matured by age 2⁺. Gamete release in all individuals of both males and females was predicted from recaptured loaches during each breeding season. The standard length of mature females was significantly larger than that of males, showing sexual size dimorphism (SSD). The maximum sizes recorded were 75.4 mm SL for females and 61.2 mm SL for males. Both males and females of immature specimens grew mainly from May to November, including the breeding season, with no significant differences in growth rates between them. After sexual maturity, both males and females grew mainly from July to October (or November), after the breeding season, and the females exhibited higher growth rates than males. Therefore, SSD of the species seems to be attributable to the different growth rates after maturity. The longevity of the loach was estimated to exceed ten years based on individual growth patterns of various sizes during the survey period. It is likely that the loach has an iteroparous life history, breeding every year, and moderate growth rates after maturity.     

Reproductive biology of Sarotherodon mossambicus (Cichlidae) in Plover Cove Reservoir,Hong Kong

Synopsis A 16-month study (August 1972 to November 1973) of Sarotherodon mossambicus in the Plover Cove Reservoir, Hong Kong revealed a sex ratio of 1:1 for small fish (below 19 cm standard length), but above this length males predominated in the population. Monthly sex composition also showed this approximately 1:1 ratio except during the months of August and September, when again males predominated. Males and females reached M₅₀ at an average length of 17.8 cm and 16.2 cm respectively. Maturity and gonosomatic index studies showed that spawning occurred from May to October with peaks in June and August, and there were at least two spawnings each year. The relationship between fecundity and standard length of females collected during both spawnings was computed to be F = 118.49L–1150.91.     

Sex ratio variation and spatial distribution of Siparuna grandiflora, a tropical dioecious shrub

Populations of dioecious plant species often exhibit biased sex ratios. Such biases may arise as a result of sex-based differences in life history traits, or as a result of spatial segregation of the sexes. Of these, sex-based differentiation in life history traits is likely to be the most common cause of bias. In dioecious species, selection can act upon the sexes in a somewhat independent way, leading to differentiation and evolution toward sex-specific ecological optima. I examined sex ratio variation and spatial distribution of the tropical dioecious shrub Siparuna grandiflora to determine whether populations exhibited a biased sex ratio, and if so, whether the bias could be explained in terms of non-random spatial distribution or sex-based differentiation in life history traits. Sex ratio bias was tested using contingency tables, a logistic regression approach was utilized to examine variation in life history traits, and spatial distributions were analyzed using Ripley's K, a second-order neighborhood analysis. I found that although populations of S. grandiflora have a male-biased sex ratio within and among years, there was no evidence of spatial segregation of the sexes. Rather, the sex ratio bias was shown to result primarily from sex-based differentiation in life history traits; males reproduce at a smaller size and more frequently than females. The sexes also differ in the relationship between plant size and reproductive frequency. Light availability was shown to affect reproductive activity in both sexes, though among infrequently flowering plants, females require higher light levels than males to flower. The results of this study demonstrate that ecologically significant sex-based differentiation has evolved in S. grandiflora. Received: 30 July 1997 / Accepted: 16 December 1997     

Reproductive biology of the Suez Canal spider crab Schizophrys aspera (H. Milne Edwards, 1834: Crustacea: Brachyura: Majidae)

A reproductive biology study of the spider crab Schizophrys aspera (H. Milne Edwards, 1834) was conducted in the Suez Canal from July 2012 to June 2013. The annual sex ratio (Male:Female) of S. aspera was female biased with values of 1:1.25. Out of the four ovarian development stages of this crab, two stages were observed in the Suez Canal throughout the whole year. The ovigerous crab’s carapace width varied from 28 to 52 mm. This crab species can spawn during most of the year in the canal water, with a peak during late spring and early winter. The fecundity of ovigerous females ranged between 2349 and 13600 eggs with a mean of 5494 ± 1486 eggs. Female crabs that reached sexual maturity exhibited a minimum carapace width varying between 22 and 46 mm, and fifty percentage of all ovigerous females showed a carapace width of 36 mm.     

长江宜昌段鲢的繁殖生物学特征

2014年3月至2016年9月在长江中下游宜昌江段共收集鲢(Hypophthalmichthys molitrix)样本433尾,进行繁殖生物学研究。该江段鲢的繁殖时间为每年的5月下旬至8月上旬,以6~7月为盛产期。繁殖群体体长310~927 mm,体重600~17 090 g,由3~7龄共5个年龄组组成,3龄群体数量上占绝对优势,占繁殖群体的45.2%。雌雄性比为1.43︰1,雌雄群体间体长-体重关系存在显著性差异(0.01P0.05)。采用Logistic方程推算出初次性成熟雌性个体体长为482.3 mm,体重为2 206.7 g;初次性成熟雄性个体体长为484.0 mm,体重1 677.5 g。卵径(1.01±0.12)mm,大小分布呈单峰型,为单批产卵型鱼类。绝对繁殖力(477 662±9 631)粒,相对繁殖力为(93.38±5.92)粒/g,绝对繁殖力随着鱼体长、体重增长而增大。与其他地理种群相比较,宜昌江段鲢总体表现为卵径相对较小而繁殖力较大。     

Feeding and reproductive biology of the currito,Hoplosternum littorale,in the Venezuelan llanos with comments on the possible function of the enlarged male pectoral spines

Synopsis The reproductive biology of roach, Rutilus rutilus, was investigated during 1980–1982 in a small tributary of the eutrophic Lake rungen, southeastern Norway. The upstream migration started in early May with medium or falling water levels and water temperatures of 6–10° C, and lasted until late May or early June. Roach (both males and females) migrating early in the season were larger than roach migrating late in the season. Males matured on average one year younger than females. The first males were mature at age 2 years, the first females were mature at age 3 years. Males were smaller than females in all age groups. There was no significant year to year variation in mean length of male and female roach in the various age-groups. Mean population fecundity during 1980–1982 was estimated to be 19 × 10⁶ eggs or 63300 eggs m^–2 of spawning area. The survival rate of eggs and small roach varied considerably due to rapid and unpredictable changes in water and silt levels. Mean annual survival rates for mature male and female roach were 0.30 and 0.52, respectively. The survival rates did not vary with age.     

西藏浪错兰格湖裸鲤种群繁殖生物学特征

2017年7月至2018年6月,于西藏自治区昂仁县浪错采集兰格湖裸鲤(Gymnocypris chui)307尾,开展种群繁殖生物学研究。结果显示,浪错兰格湖裸鲤在3～5月性成熟系数较高。雌性最小性成熟个体年龄为7龄,体长217mm,体重122.68g,成熟系数为3.92%;雄性最小性成熟个体年龄为6龄,体长198 mm,体重91.93 g,成熟系数为3.34%。其平均成熟卵径为2.18 mm,卵径分布为单峰型。绝对繁殖力为862～8 933粒/尾,平均绝对繁殖力为(2 885±2 765)粒,相对繁殖力为7～43粒/g,平均相对繁殖力为(15±11)粒/g。绝对繁殖力与体长和体重呈显著正相关,相对繁殖力与体长、体重的相关性不显著。繁殖群体性比(♀︰♂)为1︰0.967,符合1︰1比例。     

Monogamy,spawning and skin-shedding of the sea moth,Eurypegasus draconis (Pisces: Pegasidae)

Synopsis The Red Sea seamoth, Eurypegasus draconis, has a social structure that involves close pair-bonding with a monogamous mating system. The occurrence of 61 specimens, 95.1% paired, were recorded in the Gulf of Aqaba, during summers 1989 and 1990. Fourteen pairs were tagged and seven of them were seen again at least once. Cumulative location maps for tagged individuals showed that they were not territorial or site-attached, home ranges of pairs overlapped, they had low mobility, and occurred in low densities. Dissections and histological analyses showed that pairs (n = 12) were heterosexual and all individuals were sexually mature. E. draconis is sexually dimorphic. Females (n = 13) have significantly larger carapace volumes than males (n = 13). In aquaria, pairs spawned repetitively at dusk. At the peak of a spawning rise they released pelagic eggs from which embryos hatched in 24–29h at 27.2°C. Unpaired individuals probably have little opportunity to meet and mate. Close pair-bonding that ensures the availability of a mate, probably evolved as a style for increasing reproductive success in these small fish that occur in low density. E. draconis sheds its skin in one piece every 1 to 5 days.     

Floral display, pollinator visitation and reproductive success in the dioecious perennial herb Wurmbea dioica (Liliaceae)

Floral traits that increase attractiveness to pollinators are predicted to evolve through selection on male function rather than on female function. To determine the importance of male-biased selection in dioecious Wurmbea dioica, we examined sexual dimorphism in flower size and number and the effects of these traits on pollinator visitation and reproductive success of male and female plants. Males produced more and larger flowers than did females. Bees and butterflies responded to this dimorphism and visited males more frequently than females, although flies did not differentiate between the sexes. Within sexes, insect pollinators made more visits to and visited more flowers on plants with many flowers. However, visits per flower did not vary with flower number, indicating that visitation was proportional to the number of flowers per plant. When flower number was experimentally held constant, visitation increased with flower size under sunny but not overcast conditions. Flower size but not number affected pollen removal per flower in males and deposition in females. In males, pollen removal increased with flower size 3 days after flowers opened, but not after 6 days when 98% of pollen was removed. Males with larger flowers therefore, may have higher fitness not because pollen removal is more complete, but because pollen is removed more rapidly providing opportunities to pre-empt ovules. In females, pollen deposition increased with flower size 3 days but not 6 days after flowers opened. At both times, deposition exceeded ovule production by four-fold or more, and for 2 years seed production was not limited by pollen. Flower size had no effect on seed production per plant and was negatively related to percent seed set, implying a tradeoff between allocation to attraction and reproductive success. This indicates that larger flower size in females is unlikely to increase fitness. In both sexes, gamete production was positively correlated with flower size. In males, greater pollen production would increase the advantage of large flowers, but in females more ovules may represent a resource cost. Selection to increase flower size and number in W. dioica has probably occurred through male rather than female function. Received: 15 June 1997 / Accepted: 12 February 1998     

Downstream displacement and life-history traits of whitefish,Coregonus lavaretus,in a Norwegian river

Synopsis Each year from 1976 to 1985 a part of the freshwater resident whitefish,Coregonus lavaretus, in Liavatn, south-western Norway, was displaced downstreams into the sea. In the sea, they seemed to die within a short period of time. The fish appeared to be flushed downstream by autumn freshets. In age and size, but not sex, the descenders seem representative of the fish in the lake. Females were the predominant sex in the river, whereas the sex ratio did not differ from unity in the lake. Young fish were fast-growing, but the growth rate levelled off at an age of 2 years and an asymptotic length of ∼30 cm. Males matured mainly at age 1+ and females at age 2+. The gonadosomatic index decreased with age, whereas the amount of energy allocated to gonadal tissue relative to somatic tissue increased with age     

Sexual dimorphism, female reproduction and egg incubation in the oriental leaf-toed gecko (Hemidactylus bowringii) from southern China

We studied sexual dimorphism, female reproduction and egg incubation of the oriental leaf-toed gecko (Hemidactylus bowringii) from a population in southern China. The largest male and female in our sample were 60 and 57 mm snout-vent length (SVL), respectively. Males are the larger sex; sexual dimorphism in head size and tail length (TL) is evident in juveniles and adults, with males having larger heads as well as longer tails than females. Oviposition occurred between late May and late July. Females switched from laying two eggs early in the breeding season to 1-2 eggs later in the season. Clutch mass and egg mass were both independent of female SVL, whereas relative clutch mass was negatively correlated with female SVL. The previous conclusion that female H. bowringii lay a single clutch of eggs per breeding season is unlikely to be true. Thermal environments experienced by H. bowringii eggs affect incubation length as well as morphological and locomotor phenotypes of hatchlings. Hatchlings from eggs incubated at 30 degrees C were larger (SVL, tail length and body mass) and performed better in the racetrack than their counterparts from eggs incubated at 24 degrees C. Temperatures suitable for embryonic development are relatively high in H. bowringii, primarily as a consequence of the adaptive response to warm environments in southern China.     

泽蛙的性腺分化及温度对性别决定的影响

通过组织学方法观察了泽蛙(Rana limnocharis)原始生殖细胞(PGCs)的迁移、原始性腺的形成和性腺分化,并且探讨在不同的培育温度条件下性腺分化的差异。泽蛙的性腺分化有其特殊性:生殖嵴形成时,其中既有体细胞,又有原生殖细胞;无论原始性腺是分化成为精巢还是卵巢,其中都出现一个初生性腔。蝌蚪孵化后的17-34d(Gosner 26-38期)为性腺分化的敏感时期。在蝌蚪孵化后的第2d(Gosner 25期),分别用不同水温18℃±1℃、30℃±1℃、32℃±1℃、34℃±1℃培育蝌蚪,直至完成变态幼蛙(Gosner 46期)形成。自然水温23℃-25℃为对照。对照组的雌、雄性比接近1∶1(1∶1.06);18℃±1℃实验组的雌、雄比例为1.83∶1,雄性率仅35.1%(P<0.01);从30℃±1℃实验组起,雄性率提高,34℃±1℃实验组的雄性率达74.0%(P<0.01)。较高的培育温度可使泽蛙蝌蚪性别分化趋向雄性,而较低的培育温度则使蝌蚪雌性化。泽蛙的性别分化属于温度依赖型性决定(TSD)。当前全球性气候变暖对两栖类性比的稳定存在着威胁。     

Lek-like spawning,parental care and mating periodicity of the triggerfishPseudobalistes flavimarginatus (Balistidae)

Synopsis The triggerfishPseudobalistes flavimarginatus has a lek-like spawning system at Yonge Reef, Great Barrier Reef. Males migrate to a traditional mating ground where they establish territories enclosing nest sites and egg chambers. Females arrive several days later and choose a male for mating. There is biparental care of the fertilized eggs and a strict division of labour. Females appeared to be confined to the nest site by the male. Mating was semi-lunar: eggs were observed in nests several days before the new and full moons on days when high tide occurred near sunset. Differences were observed in the spawning system of another triggerfish (P. fuscus) between the Great Barrier Reef and the Red Sea. Observations of another triggerfish (Balistoides viridescens) are also reported.     

Variation in mating systems and sexual size dimorphism between populations of the Australian python Morelia spilota (Serpentes: Pythonidae)

Although adaptationist hypotheses predict a functional relationship between mating systems and sexual size dimorphism, such predictions are difficult to test because of the high degree of phylogenetic conservatism in both of these traits. Taxa that show intraspecific variation in mating systems hence offer valuable opportunities for more direct tests of evolutionary-ecological hypotheses. Based on a collation of published and unpublished records, we document intraspecific geographic variation in mating systems (presence versus absence of male-male combat) within the widely-distributed Australian python Morelia spilota. Radiotelemetric monitoring of 19 free-ranging pythons in a population in north-eastern New South Wales showed that these animals display a mating system of female defence polygyny. Previous studies on a southern population of the same species found that males engaged in long mate-searching movements, showed no overt agonistic behavior, and formed long-term (>2 months) aggregations around reproductive females. In strong contrast, our adult male carpet pythons (i) moved about relatively little (mean displacement <11 m/day) during the mating season, (ii) remained with females only briefly (<5 days), and (iii) engaged in male-male combat in the vicinity of females. This male-male combat included vigorous biting as well as ritualised wrestling matches, resulting in a high incidence of bite scars in adult males. In keeping with predictions from sexual selection theory, males attain larger body sizes than females in this population, whereas females grow larger than males in the previously-studied southern population where males do not engage in physical combat for mating opportunities.     

Reproductive behavior,egg trading,and correlates of male mating success in the simultaneous hermaphrodite,Serranus tabacarius

Synopsis Serranus tabacarius (Serranidae), the tobaccofish, is a simultaneous hermaphrodite which belongs to a group of seabasses that exhibit a wide variety of social and mating systems. The reproductive behavior of tobaccofish is similar to other hermaphroditic seabasses, with individuals assuming sex-specific spawning behaviors that allow for the assignment of male and female roles in a mating sequence. Virtually all matings involved pairs of individuals, although streaking, an alternative male mating tactic, was observed once. Pairs engage in egg trading, where individuals divide their daily clutch into a series of sequentially released parcels and take turns releasing eggs for their partner to fertilize. Individuals mate over a late afternoon spawning period with a number of partners sequentially. Larger individuals have both more total matings and more spawning partners. Egg trading is not symmetrical, the number of male and female matings for an individual in a spawning sequence is often unequal. Overall, the ratio of male to female matings increases with individual size. Large individuals are socially dominant, chase conspecifics during the reproductive period, and are more likely to end a spawning bout with a partner immediately after mating in the male role. In addition, larger individuals are less likely to reciprocate female matings by a partner, either by only mating once (as a male) in a spawning bout or by mating consecutively as a male within a series of matings. Although larger individuals show this relative specialization in the male role, they maintain their simultaneous hermaphroditism and obtain a substantial percentage of their mating success through female function. Egg trading appears to reduce the opportunity for large individuals to specialize as pure males, and thus interacts with the environmental potential for polygamy in shaping the mating system and sex allocation pattern in this species.