滇西北特有植物蓝果杜鹃的花色多态性研究?

蓝果杜鹃( Rhododendron cyanocarpum)为大理苍山特有的濒危植物,有粉色和白色两种花冠类型。为了探讨该物种花色多态性的意义,本研究调查了粉色花和白色花植株在已知的各居群的分布频率、花冠的反射光谱及其它的花部特征、有效传粉者及其访花频率与结实情况。结果表明：粉色花植株在所有调查的居群中占优势(77％~100％)。粉色花的花冠反射光谱在430 nm和650 nm有两个峰,而白色花只在430 nm有一个反射峰。同时,花特征如：花柱与柱头颜色、花冠长度、花萼长度、花梗长度以及雌雄蕊最短距离,两种花冠存在显著差异。另外,尽管熊蜂作为这两种花冠的主要传粉者,但粉红花的访花频率以及自然条件下的结实情况显著高于白色花。本研究结果推测粉红色花可能受到了稳定性选择的作用。     

Differences in floral traits and flower visitation rates in mating systems in Prunella vulgaris (Lamiaceae)

夏枯草交配系统对花特征和访花频率差异的影响 植物花特征和传粉者的访问次数与交配系统类型密切相关。唇形科植物夏枯草(Prunella vulgaris)存 在两种植株类型,分别为柱头伸出花冠和柱头在花冠内部的植株,而且两种植株的比例在不同种群中存在差异。本研究选择柱头伸出花冠外植株占绝大多数、柱头伸出花冠外植株占多数和柱头在花冠内部植株占多数的3个种群,通过比较每个种群中两种植株类型的开花物候、花形态特征、昆虫访问频率、自交能力、传粉者对结实的贡献以及近交衰退的水平,以检验花特征和传粉者访问次数与交配系统类型的关系。研究结果表明,与柱头在花冠内部的植株相比,柱头伸出花冠外的植株具有更大和更多的花,产生更多的花粉和花蜜,具有更高的访花频率,并主要通过异交产生种子。在种群水平,柱头伸出花冠外的植株占多数种群的访花频率显著高于柱头在花冠内部植株占多数的访花频率。柱头在花冠内部的植株比柱头伸出花冠外的植株具有更强的自动自交能力,在传粉者缺乏时为其提供了繁殖保障,但繁殖保障和异交率在不同种群中差异不显著,表明较低的昆虫访问能够满足夏枯草的授粉需求以产生种子,这可能与夏枯草较少的胚珠数量(每朵花仅有4个胚珠)有关。柱头在花冠内部植株的近交衰退水平低于柱头伸出花冠外植株的近交衰退水平,但两种植株类型的近交衰退水平均低于0.5,说明近交衰退不足以阻止该物种中自交的进化。综上所述,柱头在花冠内部的植株能够通过自交为夏枯草提供繁殖保障,而柱头伸出花冠外的植株能够利用昆虫传粉确保异交,表明混合交配系统在该物种中是一个稳定的状态。     

菊科12种外来植物的有性繁殖特征和入侵风险研究

菊科植物具有极强的有性繁殖能力,对外来菊科观赏植物的引进存在极高的入侵风险。本研究以武汉常见的菊科12种外来观赏植物为对象,通过有性繁殖特征调查,研究植株的花部特征、花粉活力、传粉系统、种子产量,分析各物种有性繁殖能力的差异,评估其入侵能力。结果显示,多数物种可在隔绝传粉者情况下结实;访花昆虫类型多样,共观察到26种访花昆虫,其中膜翅目蜂类是主要的传粉者;结实情况具有一定差异。综合考虑花粉活力、传粉情况和结实情况,认为黑心金光菊(Rudbeckia hirta L.)、松果菊(Echinacea purpurea(L.)Moench)、大花金鸡菊(Coreopsis grandiflora Hogg.)、蛇目菊(Sanvitalia procumbens Lam.)的有性繁殖竞争力较高,对本地传粉环境可能有较大影响。本研究对近缘物种有性繁殖特征的综合分析结果可为评估外来物种的入侵风险提供一定的参考。     

新疆产药用植物黑果枸杞有性生殖产出差异的繁殖生态学研究

由于黑果枸杞（Lycium ruthenicum）果实具有重要的保健价值,近年来倍受关注,但其野生资源正遭受着前所未有的采伐压力。目前关于影响黑果枸杞果实产量的有性生殖过程研究较少,本实验对新疆库尔勒地区6个不同生境的野生黑果枸杞居群开展了繁殖生态学观察,并对各居群的访花频率、访花昆虫种类、柱头花粉落置、胚珠数、座果率、结实率和单株果实产量等指标进行了比较分析。结果表明,访花频率与结实率、座果率具有显著正相关关系,说明传粉者是限制黑果枸杞有性生殖的关键因素之一;传粉者种类越丰富的居群其有性生殖产出越高,揭示了传粉昆虫的多样性和丰富度是影响黑果枸杞繁殖成功的重要限制因子。此外,和静县华侨农场和焉耆县霍拉山河沟的黑果枸杞居群生殖产出明显与其传粉成功率相偏离,进一步分析表明,风沙侵蚀和人为采伐对植株的破坏是影响这两个居群果实产量的重要原因。本研究结果对于野生黑果枸杞居群的保护及其人工规模栽培提供了重要的参考依据。     

草果两型植株的繁育差异研究

草果(Amomum tsaoko)是具有柱头卷曲机制的姜科植物,该研究通过观察和分析传粉者的访花行为、草果的花蜜分泌和最终的结实率,探索其花蜜分泌模式与传粉行为的相互关系,以及对其两型植株繁殖的影响。结果表明:草果两型植株的花蜜分泌在1 d花期的16:40—19:00期间达到高峰;上举型花比下垂型花能够提供更多的花蜜,下垂型花的花蜜分泌受环境温度、光照、湿度的显著影响,其结实率也显著低于上举型花。中华蜜蜂(Apis cerean cerana)是观察点频率最高的有效传粉者,在1 d花期里访花频率呈现双峰模式,访花行为受到温度和湿度的显著影响,78%或18℃较适宜访花。1 d花期中温度、湿度的变化,以及花蜜的动态分泌模式共同促进这一双峰访花模式的形成。草果花蜜分泌模式和双峰访花模式均与草果的柱头卷曲运动匹配,对吸引昆虫精确传粉、维持柱头卷曲机制有重要意义。草果两型植株之间,环境因素对它们花蜜分泌的影响显著不同,导致传粉者不同的访花行为反应和繁殖结果。适当增加居群中上举型植株数量,可能是提高产量的一个有效方法。     

鼠尾草属不同物种的雄蕊杠杆机制对传粉者空间变异的进化响应

被子植物虫媒传粉植物的物种分化通常被认为是花性状响应传粉环境(传粉者)的空间变异而发生适应性分化的结果。通过对鼠尾草属(Salvia) 3个物种(共4个居群)传粉互作系统的比较, 探索了花性状对不同传粉环境的进化响应。结果表明: 各居群的传粉者组成、主要传粉者类型及其大小各不相同, 杠杆状雄蕊及相关花部性状大小在不同居群间具有显著差异; 各居群均表现出腹部传粉和背部传粉2种传粉模式, 但背部传粉仍然是最有效的传粉方式; 居群间杠杆状雄蕊长度与传粉者体长表现出极显著的正相关, 然而花冠长与传粉者体长表现出负相关; 花冠口高度和柱头高度与传粉者胸厚也表现出一定的协同变异。鼠尾草属植物的杠杆状雄蕊及相关花部性状在传粉系统的进化过程中表现出高度的可塑性, 表明雄蕊杠杆传粉机制对传粉环境的变异非常敏感, 在该属植物的物种分化过程中具有关键作用。     

干热河谷麻疯树访花昆虫及主要传粉昆虫

膏桐为一种重要的油料作物,其种子可以提炼生物柴油,生物柴油在我国将成长为有一定规模的产业。为了增加膏桐结籽率,提高其产量,给膏桐规模化栽培方面提供传粉生物学的科学依据,于2006年对云南元江坝区半栽培膏桐(Jatropha curcas L.)居群的访花昆虫及主要传粉昆虫种类进行调查。膏桐开花示样醒目,具花香与蜜腺,花形态没有特化,这些特征使得它提供的酬物适合于不同的昆虫采食,其访花昆虫种类较丰富,共有35种访花昆虫,分属5目20科。综合访花昆虫的传粉数量,及传粉质量包括访花行为、访花频率与日活动规律等确定主要传粉昆虫,确定大头金蝇Chrysomya(Compsomyia)megacephala Fabricius、中华蜜蜂Apiscerana Fabricius、迁粉蝶(淡色型)Catopsilia pomona f.Crocale为该居群的主要传粉昆虫。3种传粉昆虫具有不同的访花习性和日活动规律。雌雄迁粉蝶日活动规律相似。访花者的组成受气象因素、开花示样及生境条件的影响。最后,探讨膏桐与访花昆虫的关系,以及主要传粉者的组成随时空变异而改变的规律。     

同域分布柽柳属两种植物的传粉生物学研究

以同域分布于新疆南部的早春开花植物短穗柽柳(Tamarix laxa Willd)和紫杆柽柳(T.androssowii Litw)为材料,对它们的开花式样、花部特征、花报酬特点、传粉特性及交配方式进行比较研究。结果表明,2种植物居群和个体水平的花期及单花寿命间存在显著差异;紫杆柽柳的居群花期比短穗柽柳短,而短穗柽柳个体花期和单花寿命比紫杆柽柳长。2种柽柳的花瓣、雌雄蕊长度、花粉胚珠数及花粉/胚珠比值(P/O)间也存在显著差异。二者的花瓣、雌雄蕊均能分泌香味,访花频率与花蜜量均存在正相关。主要传粉者在短穗柽柳上的访花频率和沉积花粉效率高于紫杆柽柳,且存在显著差异。2种植物通过自花和异花授粉均可结实,属于混合交配系统;二者的自交不亲和指数及花粉限制程度间存在显著差异;紫杆柽柳的自交亲和性高于短穗柽柳,而短穗柽柳的花粉限制指数高于紫杆柽柳。因此,2种柽柳的开花式样、花部特征及花报酬的差异,是它们在传粉者受限的早春环境中为吸引更多的访花昆虫、提高雌性繁殖率所形成的繁殖对策。     

鹅掌楸的传粉环境与性配置

近年来研究表明,动物传粉者对植物花部诱物特征（花冠形状大小,花蜜产量和花序大小）有潜在的选择作用。不同效率的传粉者可能导致植物性配置的变化,不同传粉效率的环境下,两性花植物鹅掌楸的花粉和胚珠的配置不同,居群Ｚ在主要访花者是传粉效率较低的类的传粉环境下,花粉粒小,花粉数量相对较高;另一方面胚珠投资的减少,缓解了低效的传粉（增大授粉的几率）,增加了受精的机会。相对而言,具有高效访花者的两个居群,资源较     

中国特有种——沙芥繁育系统和传粉生物学研究

运用定位观察、杂交指数、花粉-胚珠比、套袋试验和重力玻片法等方法,对沙芥自然居群和人工栽培种群的开花日动态、繁育系统和传粉习性进行了研究.结果显示:沙芥在自然居群和人工栽培种群开花日高峰分别在19:00和15:00～18:00.沙芥繁育系统为异花授粉植物.沙芥传粉媒介中风的飘移能力非常微弱;沙芥自然居群的访花昆虫有19种,分属于6个目;人工栽培种群的访花昆虫有11种,分属于6个目.意大利蜜蜂、熊蜂、黑带食蚜蝇和拟蜂食蚜蝇是两个居群共有的主要传粉昆虫,在自然居群熊蜂每天的访花频率呈双峰曲线,其中访花最高峰与开花日高峰基本重叠.     

Flower Color Polymorphism in Rhododendron cyanocarpum (Ericaceae), an Endangered Alpine Species Endemic to NW Yunnan,China

Rhododendron cyanocarpum is a narrow endemic species with pink and white floral color. In the present study, to investigate the significance of petal color morphs, we examined color morph frequencies, petal color reflectance and other associated floral characters, effective pollinators, visitation frequencies, and fruit production in the field. In all surveyed known populations, plants with pink color morph dominanted and comprised 77%-100% of individuals. Two peaks at 430 nm and 650 nm were found in the petal color reflectance of pink flowers, and only one peak at 430 nm was found in the reflectance spectrum of white flowers. In addition, color morphs were also associated with colors of style and stigma, lengths of corolla, calyx and pedicel, the closest distance between stigma and stamen, but not with style length and nectar production. Moreover, higher visitation frequency of their shared pollinators (bumblebees) and fruit production were observed of pink flowers than white flowers. Despite a briefly temporal and spacial study, we suggest that color morph frequencies, visit frequencies of bumblebees and fruit production, all favor to be stablilizing selection for the pink color morph.     

Pollinator response to flower color polymorphism and floral display in a plant with a single-locus floral color polymorphism: consequences for plant reproduction

Variation in flower color, particularly polymorphism, in which two or more different flower color phenotypes occur in the same population or species, may be affected or maintained by mechanisms that depend on pollinators. Furthermore, variation in floral display may affect pollinator response and plant reproductive success through changes in pollinator visitation and availability of compatible pollen. To asses if flower color polymorphism and floral display influences pollinator preferences and movements within and among plants and fitness-related variables we used the self-incompatible species Cosmos bipinnatus Cav. (Asteraceae), a model system with single-locus flower color polymorphism that comprises three morphs: white (recessive homozygous), pink (heterozygous co-dominate), and purple (dominant homozygous) flowers. We measured the preferences of pollinators for each morph and constancy index for each pollinator species, pollination visitation rate, floral traits, and female fitness measures. Flower color morphs differed in floral trait measures and seed production. Pollinators foraged nonrandomly with respect to flower color. The most frequent morph, the pink morph, was the most visited and pollinators exhibited the highest constancy for this morph. Moreover, this morph exhibited the highest female fitness. Pollinators responded strongly to floral display size, while probed more capitulums from plants with large total display sizes, they left a great proportion of them unvisited. Furthermore, total pollinator visitation showed a positive relation with female fitness. Results suggest that although pollinators preferred the heterozygous morph, they alternate indiscriminately among morphs making this polymorphism stable.     

Florivores prefer white versus pink petal color morphs in wild radish, Raphanus sativus

Many hypotheses suggest that pollinators act to maintain or change floral color morph frequencies in nature, although pollinator preferences do not always match color morph frequencies in the field. Therefore, non-pollinating agents may also be responsible for color morph frequencies. To test this hypothesis, we examined whether Raphanus sativus plants with white flowers received different amounts of florivory than plants with pink flowers, and whether florivores preferred one floral color over the other. We found that white-flowered plants received significantly more floral damage than pink-flowered plants in eight populations over 4 years in northern California. Both generalists and specialists on Brassicaceae preferred white petals in choice and short-term no choice tests. In performance tests, generalists gained more weight on white versus pink petals whereas specialists gained similar amounts of weight on pink and white morphs. Because our results suggest that florivores prefer and perform better on white versus pink flowers, these insects may have the opportunity to affect the frequency of color morphs in the field.     

Floral Color Polymorphism and Reproductive Success in Annatto (Bixa orellana L.)

Floral color polymorphism of annatto (Bixa orellana L.) offers a wide range of colors that are maintained in the population by either pollinators or non pollinator agents of selection. In the present study, maintenance of different floral colors was analyzed in relation to reproductive success of Bixa orellana. The different floral petal colors (white, amaranth rose, petunia purple or cobalt violet) were determined from selected plants with reflectance spectrophotometry. Phenotypic measures of other floral traits, female reproductive success, seed set, seed output and seed weight also revealed variation between different floral morphs. Records on seed set varied significantly for different floral color morphs. Maximum fruit maturation (58 %) was observed in amaranth rose and least fruit maturation (25 %) in the white morph. Seed set data indicates pollinators’ preference for more intensely colored flowers. This preference may be due to ability of the pollinators to distinguish the morphs through differentially reduced sensitivity at the green wavelengths. In flowers which received fewer insect visits, polymorphism might be maintained by self fertilization. The color morphs showed differences in Random Amplified Polymorphic DNA (RAPD) profile indicating a genetic basis for floral color variation and consequent differences in seed set. Out of 88 bands generated with nine operon primers, 70 were polymorphic. The present study provides valuable information on the influence of petal color on maternal fitness in B. orellana.     

Association of flower color with pollen reward may explain increased bumblebee visitation to the Scotch broom yellow morph

Given that pollinators usually visit flowers for hidden rewards, they need to rely on floral traits that indicate reward status (“honest signals”). However, the relationship between pollination, honest signals, and floral rewards is little documented in natural conditions. The Scotch broom (Cytisus scoparius) is an invasive shrub with polymorphism in the color of its flowers that can be yellow, orange, or red. In three areas dominated by the Scotch broom, we described the abundance of the floral morphs and estimated bumblebee (Bombus terrestris) visitation rate. We examined whether bumblebee visitation to the floral morphs was related to pollen reward. We collected flowers and classified their stamens according to their function: reward or pollen export. Then, we measured anther size and estimated pollen quantity. The yellow morph was more abundant and more visited by bumblebees than the orange and red morphs. The yellow flowers did indeed offer more pollen than the other morphs and this occurred only for rewarding anthers, suggesting that bumblebees could use yellow color as an honest signal to visit the most rewarding flowers. We discuss whether innate and/or learned preferences of bumblebees can explain why the yellow morph is more visited, pollinated, and abundant, while the other morphs are maintained at a lower frequency. This is one of the few field works that shows that variation in intra-specific floral traits is associated with variation in floral reward and pollinator visitation rate, helping to understand the foraging preferences of pollinators and the coexistence of floral morphs in nature.

Clinical trials registration: Not applicable.

     

异型花柱植物喀什补血草的传粉者功能群与花粉转移效率

异型花柱是受遗传控制的花柱多态现象, 被达尔文认为是植物通过在传粉者体表不同部位滞落花粉以促进型间花粉准确传递的一种适应。该现象虽已受到广泛关注, 但在一些花型变异较大且不稳定的传粉系统中, 不同传粉者对各花型繁殖所产生的影响仍知之甚少。该研究以分布于新疆天山南坡的一个有同长花柱共存的异型花柱植物喀什补血草(Limonium kaschgaricum)种群为研究对象, 对其花型构成及频率、传粉者及花粉转移效率等进行了调查分析。结果表明: 1)种群中除了存在雌/雄蕊长度交互对应的长(L)/短(S)花柱型花外, 还有雌/雄蕊同长的花(H型), 且各花型花的花冠口直径、花冠筒长及花粉量等参数间无差异, 但花粉纹饰和柱头乳突细胞形态具二型性。其中, H型花的花粉和柱头形态与L型花(或S型花)的一致。2)花型内和自花授粉均不亲和; 型间授粉时, 花粉和柱头形态不同的花型间亲和, 反之不亲和。3)种群内存在长/短吻两类传粉昆虫。在以短吻传粉者为主的盛花初、中期, L和H型花柱头上的异型花粉数均显著高于S型花的, 且L和S型花高位性器官间的异型花粉传递效率高于低位性器官间的; 而在以长吻传粉者为主的盛花后期, L和S型花的柱头间异型花粉数无显著差异, 且高/低位性器官间具有相同的异型花粉转移效率; 与传粉者出现时期相对应的、在花期不同阶段开放花的结实率也明显不同。4)长/短吻昆虫具明显不同的传粉功能, 短吻昆虫只能对L和H型花进行有效传粉, 且访花频率和型间花粉转移效率较低, 为低效传粉者; 而长吻昆虫对各花型均能有效传粉, 具高的访花频率和型间花粉转移效率, 为高效传粉者。因为长吻昆虫的阶段性出现所形成的不稳定传粉系统, 使低效的短吻昆虫可能会成为种群中花型变异的驱动力, 并使S型花受到更大的选择压力。H型花克服了柱头缩入的弊端, 可能会成为不稳定传粉系统下的一个替代花型而持续存在。     

Discovery of gynoecium color polymorphism in an aquatic plant

Flower color polymorphlsm exhibited by natural populations provides an opportunity for understanding the evolutionary mechanisms contributing to the diversity of floral morphology.However,little is known about the color polymorphism of female organs in flowering plants.Here we report gynoecium color polymorphism in Butomus umbellatus (Butomaceae),an emergent,aquatic monocot.Populations from Mishan,northeastern China comprised two morphs; gynoecia are either pink,as observed in other areas,or white.We measured floral traits and female fecundity in the two gynoecium color morphs in the field.There was no significant difference in plant height,pedicel length,and flower size including petal,sepal and gynoecium between the two morphs,but plants with pink gynoecia had wider inflorescence stalks,larger inner whorl anthers and produced more pollen and ovules than those with white gynoecia.Correspondingly,we found that seed production was significantly higher in the pink than in the white morph.This new finding suggested selection against white gynoecia in part because of low fecundity,consistent with the rarity of the white gynoecium morph in this species.     

Pollinator visitation in populations of tristylous Eichhornia paniculata in northeastern Brazil

Summary The frequencies of floral morphs in populations of tristylous Eichhornia paniculata often deviate from the theoretical expectation of equality. This variation is associated with the breakdown of tristyly and the evolution of self-fertilization. Differences in morph frequencies could result from selection pressures due to variable levels of insect visitation to populations and contrasting foraging behavior among the floral morphs. We estimated pollinator densities in 16 populations and quantified visitation sequences to morphs in five populations of E. paniculata in northeastern Brazil. Foraging behavior among floral morphs was measured as the frequency of visits to morphs relative to their frequency in the population (preference) and number of flights between inflorescences of the same versus different morphs (constancy). Pollinator density (number/m²/minute) was not correlated with population size, plant density or morph diversity. Pollinator densities varied most among populations of less than 200 plants. Whether pollinators discriminated among the morphs, depended on whether they primarily collected nectar or pollen. In four populations, nectar-feeding bees (Ancyloscelis and Florilegus spp.) and butterflies showed no consistent preference or constancy among the morphs. In contrast, pollen-collecting bees (Trigona sp.) visited a lower proportion of longstyled inflorescences than expected and tended to visit more mid-and short-styled inflorescences in succession, once they were encountered. Pollinator constancy for morphs did not result from differences in inflorescence production or spatial patchiness among the morphs. Although non-random pollinator visitation to morphs in heterostylous populations could potentially affect mating and hence morph frequencies, the observed visitation patterns in this study do not provide evidence that pollinators play a major role in influencing floral morph frequencies.     

Direct and indirect selection on floral pigmentation by pollinators and seed predators in a color polymorphic South African shrub

The coexistence of different color morphs is often attributed to variable selection pressures across space, time, morph frequencies, or selection agents, but the routes by which each morph is favored are rarely identified. In this study we investigated factors that influence floral color polymorphisms on a local scale in Protea, within which approximately 40% of species are polymorphic. Previous work shows that seed predators and reproductive differences likely contribute to maintaining polymorphism in four Protea species. We explored whether selection acts directly or indirectly on floral color in two populations of Protea aurea, using path analysis of pollinator behavior, nectar production, seed predation, color, morphology, and maternal fecundity fitness components. We found that avian pollinators spent more time on white morphs, likely due to nectar differences, but that this had no apparent consequences for fecundity. Instead, the number of flowers per inflorescence underpinned many of the reproductively important differences between color morphs. White morphs had more flowers per inflorescence, which itself was positively correlated with nectar production, seed predator occurrence, and total long-term seed production. The number of seeds per plant to survive predation, in contrast, was not directly associated with color or any other floral trait. Thus, although color differences may be associated with conflicting selection pressures, the selection appears to be associated with the number of flowers per inflorescence and its unmeasured correlates, rather than with inflorescence color itself.     

Flower-visiting bees and the breakdown of the tristylous breeding system of Eichhornia azurea (Swartz) Kunth (Pontederiaceae)

Populations of Eichhornia azurea (Swartz) Kunth (Pontederiaceae) are often composed of three floral morphs that differ in style length and anther position. Hence, E. azurea is described as tristylous. For sexual reproduction the plant requires specialized pollinators able to transfer pollen from flowers with long-, mid-, or short-level anthers to flowers with long-, mid-, or short-styles, respectively. This is because within a floral morph, self-incompatibility is the rule. Populations of E. azurea were studied from six localities in south-eastern Brazil (São Paulo and Minas Gerais). The frequencies of floral morphs, floral morphology and flower-visiting bees were recorded in each population. Ten different bee species were observed visiting plants. Four of them were considered generalist bees and not appropriate for legitimate pollination of the three floral morphs. Another three species were considered opportunists and only three species were considered to be potential pollinators. At the coastal region (Juréia), the plant population lacked the short-styled morph and the mid-styled morph and exhibited a semi-homostylous condition, in which the low-level anthers were adjacent to the stigma. This morph showed high level of self-compatibility. The disappearance of the short-styled morph from this region is likely correlated with the absence of Ancyloscelis gigas Friese, a specialized long-tongued bee that is oligolectic on this plant in other localities.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 77 , 499–507.