Sexual selection and assortative mating by size and their roles in the maintenance of a polymorphism in Swedish Littorina saxatilis populations

Two independent components of mating behaviour, sexual selection and assortative mating, were studied in two allopatric morphs, one sheltered boulder shore form (S-morph) and one exposed cliff shore form (E-morph), of Littorina saxatilis from the west coast of Sweden. Sexual selection was studied by comparing the sizes of copulating and non-copulating snails in the field. Size assortative mating was studied by collecting copulating pairs in the field, while assortative mating between morphs was investigated by bringing the pure morphs together in intermediary habitats and then noting the matings. The S-morph mated randomly in relation to size in two of the studied populations and exhibited a trend towards size assortative mating in a third, while the E-morph showed size assortative mating in both studied populations. The microdistribution of sizes of snails on the shores could not explain all the size assortative mating found, and instead it is argued that a size-based mate rejection behaviour also contributes to the assortative mating in at least some of these populations. There was sexual selection on size in both males and females in the S-morph, with large individuals being favoured as mates. In contrast, copulating snails of the E-morph were smaller than non-copulating ones. The significantly different sexual selection intensities between the two morphs may help to explain the size differences between them. There was random mating between the E- and the S-morphs of L. saxatilis, which suggests no incipient reproductive isolation between morphs on Swedish rocky shores. This is in agreement with earlier studies of Swedish populations, but is in contrast to the situation found in other geographical areas.     

Mate search and aggregation behaviour in the Galician hybrid zone of Littorina saxatilis

In Galician rocky shores two ecotypes of the snail L. saxatilis can be found in sympatry. A ridged and banded ecotype (RB-morph) and a smooth and unbanded ecotype (SU-morph) overlap in midshore with the production of some hybrids. The distinct morphs mate assortatively and there is evidence of a partial reproductive barrier between them. This sexual isolation is caused by a nonrandom microdistribution and mate choice behaviour. Mucus trail-following, movement rate and aggregation behaviour were studied to determine their roles in the mating behaviour and sexual isolation of this species. Morph-specific mucus trail-following could not, in our experiments, explain either of these two processes. The reasons for the aggregation of morphs were investigated by Monte Carlo simulations of data from natural populations, which showed that size aggregation (refuge sizes fit different sized morphs differently) could explain only about 36% of the morph aggregation in adult snails. In the laboratory, morph aggregation was still present, and simulations suggested that size aggregation was the possible explanation. Thus, morph aggregation in Galician L. saxatilis has to be explained also by other causes in addition to size aggregation. These may be a combination of contrasting preferences for barnacle and mussel patches in the two morphs, and possibly longer copulation and pair formation time with similar sized snails of the same morph. Thus aggregation behaviour, but not trail-following, contributes to incipient reproductive isolation and perhaps sympatric speciation in Galician L. saxatilis populations.     

Thermal advantage of pale coloured morphs of the snail Arianta arbustorum (Helicidae, Pulmonata) in alpine habitats

In alpine grasslands pale colour morphs of the snail Arianta arbustorum are more frequent than dark ones As pale morphs absorb less solar radiation, they may forage for longer in sunlight and/or have a lower mortality risk from overheating This hypothesis was tested Equal numbers of pale and dark morphs were kept in enclosures in an alpine meadow During the day, more pale morphs were seen than dark ones, the latter obviously remaining hidden The difference was not significant in enclosures set up in a nearby forest, confirming that the inequality in behaviour depends on the amount of sunlight Dark snails are on average warmer than pale ones
Experiments were also conducted in grassland on a mountain slope at altitudes between 1200 and 2000 m Snails were marked with a paint which fades in light, and released When recaptured several days later, the marks were more faded in pale morphs than in dark, suggesting that they had been more exposed to sunlight, supporting our hypothesis The difference in fading was more pronounced at high than at low altitude     

Survival,behaviour and spatial distribution of shell morphs in a population of the snail Brephulopsis bidens (Pulmonata)

Summary Microspatial variation of banded and unbanded shell morphs frequencies as well as number of individuals per m², mortality, migration and burrowing into the ground were examined in a population of snail Brephulopsis bidens found in South Crimea mountains (USSR). Differential values of relative survival of morphs were determined by their thermotolerance. The relative survival of the banded morph was lower at the west sites of population area (W=0.273), and increased gradually up to 1 at the east sites. Survival of the banded morph was dependent on its burrowing activity. Differences in relative survival of morphs decreased parallel with increasing general mortality of snails.Burrowing activity and intensity of migration of the banded morph were significantly higher than that in unbanded. In experiments with artificial shaded sections, the banded morph preferred shaded sections, whereas unbanded chose illuminated sites. All these differences in behaviour probably form the main factors for microspatial variation of morph frequencies.     

花柱卷曲性的维持及功能性别特化

花柱多态型的型比通过选型交配形成的负频率依赖的选择来维持。种群空间格局对于频率依赖选择所维持的花柱多态型是至关重要的。该研究使用摆放实验构建不同型比的马来良姜(Alpinia mutica)人工种群, 以评价花柱卷曲性促进选型交配的功能。使用邻域模型调查了云南草蔻(Alpinia blepharaocalyx)种群中的目标植株的坐果数、结籽数及其邻域中花序的数量和型偏以探讨在局域尺度上目标植株的雌性适合度是否受负频率依赖的选择。通过比较云南草蔻上举型和下垂型各繁殖性状的差异以及两型的功能性别的计算以评估两型功能性别可能存在的特化趋势。摆放实验结果说明花柱卷曲性形成的二型种群可以促进型间花粉传递。在局域尺度上, 云南草蔻两型倾向于同型聚集分布, 这一分布特点反映出其克隆生长特性。统计结果说明: 邻域中异型花粉供体相对丰富度对两型目标植株都无影响; 目标植株雌性适合度在邻域中不受负频率依赖选择的影响。这一结果并不支持负频率依赖的选择在该研究尺度上是影响种群型比结构的主要机制。云南草蔻两型个体在花期和果期的繁殖指标上不存在显著差异; 功能性别计算结果显示选型交配是种群内唯一的交配模式时, 下垂型功能性别偏雌性而上举型功能性别偏雄性。这一功能性别特化的趋势可能是通过对上举型的雄性功能的选择而造成的, 并可能与种群型结构相关。当功能性别计算只考虑自交而忽略近交衰退时, 种群功能性别偏向雌性。     

麦长管蚜虫龄鉴别特征

【目的】为明确麦长管蚜Sitobion avenae (Fabricius)虫龄鉴别特征, 达到快速鉴别的目的。【方法】在成像观察的基础上, 测定无翅型和有翅型个体不同虫龄的体长、 体宽、 头壳宽、 触角长、 腹管长和后足胫节长6项指标。【结果】麦长管蚜不同翅型个体的体长、 体宽、 头壳宽、 触角长、 腹管长和后足胫节长在虫龄间均存在显著差异, 其中体长、 体宽、 头壳宽和触角长在相邻虫龄之间重叠程度大, 后足胫节长的重叠百分比极小或无重叠; 除有翅型个体4龄若蚜和成蚜之间存在13.93%的重叠外, 腹管长在不同翅型的其他相邻虫龄之间重叠百分比均极小或无重叠, 说明后足胫节长和腹管长可作为虫龄鉴定的主要特征。翅、 触角和尾片的其他外部形态特征在虫龄间也存在一定差异： 3-4龄有翅型若蚜和成蚜虫个体前胸的膨大程度及其翅的长度明显大于同一龄期的无翅型个体, 可用于蚜虫翅型的分辨以及3-4龄有翅若蚜和成蚜的鉴别; 麦长管蚜1和2龄若蚜触角均为5节, 3-4龄若蚜和成蚜的触角均为6节; 同时, 除了成蚜具有完整的尾片外, 1-4龄若蚜尾片均不发达, 说明触角的节数和尾片的发达程度可作为麦长管蚜不同龄期形态鉴别的辅助特征。【结论】以腹管和后足胫节作为麦长管蚜虫龄鉴别的主要特征, 配合其他辅助特征, 如翅的大小、 触角的节数以及尾片的发达程度等, 可达到快速鉴别不同翅型不同龄期蚜虫的目的。     

Wing dimorphism in the migratory locust,Locusta migratoria: differentiation of wing morph and phase polyphenism

A short‐winged morph was recently discovered in the migratory locust, Locusta migratoria. It is different from the normal, long‐winged morph not only in forewing length but also in hind femur length, displaying a dimorphism. To understand the significance of this dimorphism, other morphological characters were compared between the two morphs, and the time of differentiation of wing‐pad length was investigated. Wing weights were heavier in the long‐winged morph than in the short‐winged morph. This result showed that the short‐winged morph is not formed by a failure of wing expansion. No obvious morph‐specific differences were observed in wing venation, but wing allometry studies indicated that the distal areas of the fore‐ and hindwings were disproportionally reduced in the short‐winged morph compared to the long‐winged morph. The morphological differentiation of the wing pad between the two morphs was observed at the penultimate nymphal stage. The flight muscle was well developed in the two morphs, and no sign of flight muscle histolysis was detected in either morph after adult emergence. An analysis of adult body dimensions suggested that the density‐dependent phase shifts known for the long‐winged morph of this locust were also exhibited by the short‐winged morph, demonstrating that these shifts are not specific to the migratory long‐winged morph.     

Recent speciation between sympatric Tanganyikan cichlid colour morphs

Lake Tanganyika, Africa's oldest lake, harbours an impressive diversity of cichlid fishes. Although diversification in its radiating groups is thought to have been initially rapid, cichlids from Lake Tanganyika show little evidence for ongoing speciation. In contrast, examples of recent divergence among sympatric colour morphs are well known in haplochromine cichlids from Lakes Malawi and Victoria. Here, we report genetic evidence for recent divergence between two sympatric Tanganyikan cichlid colour morphs. These Petrochromis morphs share mitochondrial haplotypes, yet microsatellite loci reveal that their sympatric populations form distinct genetic groups. Nuclear divergence between the two morphs is equivalent to that which arises geographically within one of the morphs over short distances and is substantially smaller than that among other sympatric species in this genus. These patterns suggest that these morphs diverged only recently, yet that barriers to gene flow exist which prevent extensive admixture despite their sympatric distribution. The morphs studied here provide an unusual example of active diversification in Lake Tanganyika's generally ancient cichlid fauna and enable comparisons of speciation processes between Lake Tanganyika and other African lakes.     

A stable,genetically determined colour dimorphism in the dung beetle Aphodius depressus: patterns and mechanisms

1. Melanism – the occurrence of dark morphs – in insects has been attributed to differences in, among other things, thermoregulation and immune defence. Dark individuals are hypothesised to perform better in colder areas, and to exhibit stronger melanin‐based immune defence. 2. In the present study, the geographical distribution of two colour morphs in Aphodius depressus (Kugelann), its climatic correlates, and temporal stability was described. Underlying mechanisms were then targeted through experiments: the inheritance of colour through controlled crosses, heating rates by thermal imaging, physiological tolerance by critical thermal limits, and immune efficiency by melanisation of implants. 3. In A. depressus, colour appears inherited by simple Mendelian principles, with red dominating over black. The frequency of two colour morphs forms a large‐scale cline. In the South West of Finland, all individuals are black, whereas, in the North East, most are red. This pattern has remained constant over 13 years (1996–2008). 4. The geographical pattern was not attributable to thermoregulation: black morphs were more abundant in warmer rather than colder parts of the country. In experiments, we found no differences in the heating rate of the two morphs, or in their upper temperature maxima. Neither did the morphs differ in their response to artificial objects inserted in their haemolymph. 5. Overall, colour variation in A. depressus occurs as a stable, genetically determined dimorphism, governed by Mendelian inheritance. Yet, no support for prevailing theory of factors sustaining melanism was found. The reasons for colour polymorphism in insects may thus be complex, and should be sought on a case‐by‐case basis.     

Activity and weight loss in relation to solar radiation in the polymorphic land snail Cepaea nemoralis

Shell spectral reflectance, activity and weight loss in the land snail Cepaea nemoralis were examined to test whether solar radiation has different effects on the behavioural and physiological responses of different morphs. A uniform area from the empty shells of different morphs was cut and a spectrophotometer was used to measure the spectral reflectance at wavelengths from 220 nm to 800 nm. Snails were put into cages made of mesh hardware cloth, and their activities were observed from dawn onwards on two hot, dry days. Weight loss of snails under shade and under direct sunlight was also measured.
The results show that unbanded morphs reflect more light than five-banded ones, but the yellow morphs reflect only a little more than pink morphs. Five-banded morphs became inactive more quickly than unbanded ones from dawn onwards, but the differences in activity patterns were not significant between pink and yellow morphs. There are significant differences in percent weight loss between snails placed under direct sunlight and under shade. The weight loss of different morphs under shade was not statistically different. But when exposed to sunlight, five-banded morphs lost more weight than pink and yellow unbanded morphs.
Because of their lower reflectance of solar radiation, the five-banded morphs are, in a hot, arid climate, at a selective disadvantage compared to unbanded morphs. However, they can avoid such selective disadvantage by actively seeking a shaded area, as all other morphs do in the field. Such behavioural habitat selection could help the maintenance of genetic polymorphisms in natural populations.     

Dimorphic migration,growth, and fecundity in a seasonally split population of Littorina brevicula (Mollusca: Gastropoda) on a boulder shore

Littorina brevicula (Philippi) is an abundant herbivorous gastropod species inhabiting intertidal zones of the north-western Pacific and has internal fertilization with planktonic eggs and a larval stage. A population of L. brevicula on a shore in Amakusa, Japan, splits into an upper and a mid shore sub-population during the mating season in winter, while all individuals occurred in the upper zone in summer. Transplant and recapture experiments have shown that snails from each sub-population have a distinct pattern of seasonal migration, suggesting that the snail population consists of two behavioral morphs. To explore the relationship between migration pattern and life history characteristics in the snails of the two migration morphs, monthly quantitative samplings and a mark-release and recapture survey were carried out for the population of L. brevicula over a 1-year period. In autumn, some of the adults migrated downward to the mid shore and formed the lower sub-population from October to April. Migration between the upper and lower sub-populations was minimal from December to February, when L. brevicula copulate actively. The shell growth rates of the snails in the lower zone were slightly higher than those in the upper zone, but the shell width of females was not a good predictor of the number of mature ova they contained. The number of mature ova was not significantly different between the females of the two migration morphs. In addition, the mortality of marked snails did not differ significantly between the upper and lower zones. Thus, no evidence was obtained to indicate a difference in the reproductive fitness between the two migration morphs.     

不同小麦品种对有翅与无翅型禾谷缢管蚜生长发育与繁殖的影响

室内采用水培小麦法饲养禾谷缢管蚜Rhopolosiphum padi(L.),比较了有翅与无翅型禾谷缢管蚜若虫发育历期、成虫寿命、繁殖力和日均体重增长量.结果表明,不同小麦品种上有翅型和无翅型若虫发育历期均存在显著差异;同时产若蚜数量、每代产若蚜数和腹中胚胎数均存在显著差异,而成蚜寿命、产若蚜历期和产若蚜代数差异不显著...     

Influence of shell colour on the mortality rate of the land snail Arianta arbustorum under different microclimatic regimes

The mortality of phenotypic shell colour morphs and age classes of the snail Arianta arbustorum in several microclimatic conditions was recorded. An analysis of variance was performed on five factors: adaptation temperature, relative humidity, shell colour, age class and test temperature. There were no significant differences in the mortality between different adaptation temperatures or relative humidities, but the interaction of these two factors was highly significant. There were significant differences in mortality rate between test temperature and age class. The mortality of the brown morph was higher than the yellow one at all adaptation temperatures (overall, P < 0.05). There were no significant differences between the mortality rates of the two morphs at different relative humidities. The mortality of the brown morph was higher than that of the yellow at six out of seven test temperatures. Juvenile snails survived significantly better than adults at all test temperatures.     

Shell Temperature, Activity and Resistance to Desiccation in the Polymorphic Land Snail Cepaea Vindobonensis

Shell temperature during the morning hours, and the 24-houractivity pattern have been studied in the two distinct morphsof the polymorphic land snail Cepaea vindobonensis. Shell temperaturesbetween the two morphs differed significantly when snails wereplaced in the sun and the temperature difference was about 1°C. Activity observations in the field and in the laboratory revealedthat adult dark-banded snails were in general less active thanboth morphs of juveniles and adult faint-banded snails during sunnymornings or under severe heat load. In the field and duringcloudy mornings no statistically significant differences betweenmorphs were seen. Resistance to desiccation was studied among the two morphs ofthe same population in which activity was observed and anotherpopulation coming from a more northern and more humid habitat.A clear intraspecific difference was found in resistance todesiccation. Snails from the southern population living in amore arid habitat were more resistant than snails from the northernpopulation. Within the same population percentage water lossdid not differ significantly between the two morphs but thefaint-banded snails seemed better adapted to aridity since onlyin these snails was no difference detected in relative bodywater after desiccation. (Received 28 July 1997; accepted 20 June 1998)     

The evolution of phally polymorphism in Bulinus truncatus (Gastropoda,Planorbidae): the cost of male function analysed through life-history traits and sex allocation

In the hermaphrodite freshwater snail Bulinus truncatus, two sexual morphs, euphallic (regular hermaphrodites) and aphallic individuals without a male copulatory organ, co-occur at various ratios in natural populations. Both aphallic and euphallic individuals can reproduce by selfing, but when outcrossing aphallic individuals can only play the female role. A comparison of life-history traits and sex allocation in these two forms provides the opportunity to investigate the evolution and maintenance of sexual polymorphisms. This study was performed to test whether a reallocation of resources from the lost male function to the female function occurs in aphallic snails at the level of both sex organs (sex allocation) and life-history traits. In a first experiment we compared life-history traits over a whole life-cycle under selfing between the two sexual morphs. In a second experiment, the sex organs were weighed to test for a difference in sex allocation between the two morphs. No difference in resource allocation to female function between the two morphs was observed in either experiment. This is in contrast to patterns frequently observed in sexually polymorphic plants, and in a previous study performed on aphally in the same snail species. We discuss the genetic and physiological hypotheses that could explain these results, and their consequences for the evolution and maintenance of phally polymorphism in B. truncatus.     

有翅型和无翅型大豆蚜卵巢和胚胎发育的差异

【目的】比较大豆蚜Aphis glycines有翅型和无翅型个体的卵巢发育,为从生理生化角度研究蚜虫翅型分化发生的繁殖适应性提供依据。【方法】在卵巢形态显微镜观察基础上,比较有翅型和无翅型大豆蚜卵巢小管数量、胚胎总数量、成熟胚胎数量以及卵巢小管中最大胚胎体积及其发育速率。【结果】有翅型和无翅型大豆蚜的3龄和4龄若蚜以及成蚜均有2个卵巢/雌,大多数蚜虫每个卵巢包含4条卵巢小管,可见一个卵巢包含5条卵巢小管的现象。有翅型和无翅型个体卵巢中胚胎总数量和成熟胚胎数量以及最大胚胎体积随发育时间增加均显著增大,但有翅型个体胚胎总数量和成熟胚胎数量以及最大胚胎体积均显著小于同一发育阶段无翅型个体。有翅型和无翅型的3龄和4龄若蚜以及成蚜卵巢中胚胎总数量与后足胫节长度均呈显著正相关关系。有翅型和无翅型大豆蚜卵巢小管中最大胚胎体积随发育时间均呈指数增长,但有翅型个体最大胚胎体积显著小于无翅型个体。【结论】有翅型大豆蚜相比于无翅型个体存在卵巢发育延迟现象,卵巢发育程度的差异可能与翅的发育相关。     

More Ornamented Males Exhibit Increased Predation Risk and Antipredatory Escapes,but not Greater Mortality

Secondary sexual traits not only confer benefits to their bearer through increased mate acquisition, but may also have inherent costs, including the attraction of predators. Here, we examined the relationship between conspicuous secondary sexual traits and predation costs using two male morphs of Schizocosa wolf spiders: brush‐legged and non‐ornamented. In the field, we ran two predation experiments using artificial enclosures to directly test mortality costs of predation on the two male morphs. Using a natural predator, a larger wolf spider in the genus Hogna, we found no difference in predation on brush‐legged vs. non‐ornamented males. However, predation was depends on environmental conditions. More individuals were preyed upon at night (vs. during the day) and on rock litter (vs. leaf litter), but the two male morphs were preyed upon equally to each other across environmental treatments. A laboratory experiment incorporated staged interactions between a single predator (Hogna) and each male morph to examine finer details of predation events. Again, we found no differential mortality between brush‐legged and non‐ornamented males. However, brush‐legged males were attacked sooner and were more likely to escape the attack. Our results show an association between sexual ornamentation and predation risk as well as escape behavior.     

Genetic and demographic variation among colour morphs of cabrilla sea bass

The Mediterranean cabrilla sea bass Serranus cabrilla exhibits two colour morphs (red and yellow) that appear to be depth segregated, with yellow individuals found below 20 m and red ones found above 20 m. Morphology and otolith analyses show that yellow fish are larger and older. There were similar allelic frequencies between colour morphs, but significant differences in the genotypic frequencies with an increase of excess of heterozygotes in yellow specimens. It is proposed that the yellow fish are older and develop from younger red fish that have migrated to deeper water.     

Phenotypic Plasticity of the Introduced New Zealand Mud Snail,Potamopyrgus antipodarum,Compared to Sympatric Native Snails

Phenotypic plasticity is likely to be important in determining the invasive potential of a species, especially if invasive species show greater plasticity or tolerance compared to sympatric native species. Here in two separate experiments we compare reaction norms in response to two environmental variables of two clones of the New Zealand mud snail, Potamopyrgus antipodarum, isolated from the United States, (one invasive and one not yet invasive) with those of two species of native snails that are sympatric with the invader, Fossaria bulimoides group and Physella gyrina group. We placed juvenile snails in environments with high and low conductivity (300 and 800 mS) in one experiment, and raised them at two different temperatures (16°C and 22°C) in a second experiment. Growth rate and mortality were measured over the course of 8 weeks. Mortality rates were higher in the native snails compared to P. antipodarum across all treatments, and variation in conductivity influenced mortality. In both experiments, reaction norms did not vary significantly between species. There was little evidence that the success of the introduced species is a result of greater phenotypic plasticity to these variables compared to the sympatric native species.     

MolMovDB: analysis and visualization of conformational change and structural flexibility

The Database of Macromolecular Movements (http://MolMovDB.org) is a collection of data and software pertaining to flexibility in protein and RNA structures. The database is organized into two parts. Firstly, a collection of 'morphs' of solved structures representing different states of a molecule provides quantitative data for flexibility and a number of graphical representations. Secondly, a classification of known motions according to type of conformational change (e.g. 'hinged domain' or 'allosteric') incorporates textual annotation and information from the literature relating to the motion, linking together many of the morphs. A variety of subsets of the morphs are being developed for use in statistical analyses. In particular, for each subset it is possible to derive distributions of various motional quantities (e.g. maximum rotation) that can be used to place a specific motion in context as being typical or atypical for a given population. Over the past year, the database has been greatly expanded and enhanced to incorporate new structures and to improve the quality of data. The 'morph server', which enables users of the database to add new morphs either from their own research or the PDB, has also been enhanced to handle nucleic acid structures and multi-chain complexes.