THE EXTENT OF INTROGRESSION OUTSIDE THE CONTACT ZONE BETWEEN NOTROPIS CORNUTUS AND NOTROPIS CHRYSOCEPHALUS (TELEOSTEI: CYPRINIDAE)

The cyprinid fishes, Notropis cornutus and N. chrysocephalus, hybridize in a long, narrow zone in the midwestern United States. To quantify the extent of introgression of genetic markers outside of this zone, samples were collected along transects starting near the region of contact (as defined by morphological characters), followed by samples progressively more distant. Diagnostic allozymic and mitochondrial DNA (mtDNA) restriction site markers were used to estimate the extent of introgression outside of the zone, while polymorphic allozyme and mtDNA markers were used to evaluate the potential for gene flow among populations within transects. Analysis of populations from the northern transect provided evidence for differentiation of populations for some of the markers; however, on average, enough gene flow has occurred to overcome substantial differentiation. Introgressed mtDNA and allozyme haplotypes were rare and found only in the population closest to the contact zone. The rarity of introgressed alleles in the more northern populations is consistent with the recent origin of these populations after the Wisconsin glaciation (less than 12,000 years bp) and/or selection maintaining the northern boundary of the contact zone. Analysis of populations from the southern transect revealed evidence for population subdivision but no evidence for introgression at the diagnostic allozyme loci; however, nearly all individuals from this transect possessed introgressed mtDNA haplotypes, with samples furthest from the contact zone exhibiting the highest frequencies of introgression. Patterns of variation for one of the polymorphic allozyme markers (Est-A) and introgressed mtDNAs were highly correlated, suggesting that allozymic heterogeneity at this locus is also the result of introgression. The most likely explanation for these data is that these introgressed haplotypes are indicators of a more southern position of the contact zone during the Pleistocene, with the contact zone shifting northward with the recession of the glacial front. Such movement implicates selection in the maintenance of distributional limits of these species, and hence, the width and position of the contact zone.     

SEXUAL SELECTION AGAINST HYBRIDS BETWEEN SYMPATRIC STICKLEBACK SPECIES: EVIDENCE FROM A FIELD EXPERIMENT

Sexual selection against viable, fertile hybrids may contribute to reproductive isolation between recently diverged species. If so, then sexual selection may be implicated in the speciation process. Laboratory measures of the mating success of hybrids may underestimate the amount of sexual selection against them if selection pressures are habitat specific. Male F₁ hybrids between sympatric benthic and limnetic sticklebacks (Gasterosteus aculeatus complex) do not suffer a mating disadvantage when tested in the laboratory. However, in the wild males choose different microhabitats and parental females tend to be found in the same habitats as conspecific males. This sets up the opportunity for sexual selection against male hybrids because they must compete with parental males for access to parental females. To test for sexual selection against adult F₁ hybrid males, we examined their mating success in enclosures in their preferred habitat (open, unvegetated substrate) where limnetic males and females also predominate. We found significantly reduced mating success in F₁ hybrid males compared with limnetic males. Thus, sexual selection, like other mechanisms of postzygotic isolation between young sister species, may be stronger in a wild setting than in the laboratory because of habitat-specific selection pressures. Our results are consistent with, but do not confirm, a role for sexual selection in stickleback speciation.     

REPRODUCTIVE ISOLATION AND INTROGRESSION BETWEEN NOTROPIS CORNUTUS AND NOTROPIS CHRYSOCEPHALUS (FAMILY CYPRINIDAE): COMPARISON OF MORPHOLOGY,ALLOZYMES, AND MITOCHONDRIAL DNA

Hybrid zones in fluvial fishes may be heterogeneous from drainage to drainage. The comparison of data from morphology, allozymes, and mitochondrial DNA (mtDNA) indicates variability in the causes and degree of restriction of gene flow between Notropis cornutus and Notropis chrysocephalus. Allozyme marker loci show frequency-dependent introgression; i.e., the rarer species, whichever it is at a particular locality, tends to exhibit a higher proportion of introgressed alleles. Unlike allozymes, introgression of mtDNA haplotypes varies geographically. In westward-flowing Michigan drainages, N. cornutus mtDNA haplotypes are more common in F₁ hybrids and backcrosses, independent of parental frequencies. In eastward-flowing Michigan drainages, N. chrysocephalus mtDNA is more common in F₁ hybrids and backcrosses; this pattern may be due to local ecological effects or frequency-dependent introgression. Morphological data alone are not sufficient to distinguish all classes of hybrids. The lack of concordance of morphological, allozymic, and mtDNA introgression patterns implies operation of one or two factors: 1) geographically variable patterns of selection against different hybrid and backcross combinations or 2) genetic differences between Michigan populations inhabiting eastward- and westward-flowing drainage systems accumulated during historical isolation.     

白鱼属鱼类的系统发育(鲤形目:鲤科)

白鱼属(Anabarilius Cockerell)是我国特有的鲤科鱼类,主要分布于云南东部、中部和四川南部。分布范围不大,但种的分化强烈。 Regan(1904,1908, 1918)最先报道四种白鱼,但均置于Barilius属。尔后,Cockerell(1923)以Barilius andersoni Regan为模式种建立白鱼属;Nichols(1927)、张孝威(1944)、易伯鲁、吴清江(1964)、刘振华、何纪昌(1983)先后记述了部分种和亚种。陈银瑞、褚新洛(1980)在系统整理的基础上,澄清了白鱼属属级分类上的混乱,记述了三新种和一新亚种。何纪昌、王重光(1984)用数值分类法探讨了白鱼属的分类,报道了二新种和一新亚种。至此,白鱼属共包括15个种和亚种。     

云南鲤属(Cyprinus)鱼类的分类整理

关于鲤属鱼类的分类,过去已有两次比较系统的研究,但对亚属的划分、种下阶元的判定等仍有争议。原因是分类所循的外形性状变异较大,且多互相重叠。本文试从骨骼比较入手,寻找新的、较为稳定的分类依据。经比较分析,鲤属鱼类的第一脊椎横突、上颌骨、上筛骨、额骨、枕骨突、犁骨、下咽骨和下颌骨等存在明显差异,可作为划分亚属和种的鉴别特征。据此重新分类整理,认为Mesocyprinus亚属仍能成立,首次把产于洱海的厚唇鲤cyprinus crassilabris Chen et Hwang归入杞麓鲤Cyprinus carpio chilia Wu et al.的同物异名;Cyprinus pellegrini pellegrini Tchang,Cyprinus pellegrini barbatus Chen et Hwang,Cyprinns yunnanensis yunnanensis Tchang和Cyprinus yunnanensis daliensis Chen et Hwang在骨骼上有明显分化,由亚种提升为各自独立的种。整理后云南共有鲤属鱼类12个种和亚种,以骨骼特征做出检索表。     

REINFORCEMENT IN CHORUS FROGS: LIFETIME FITNESS ESTIMATES INCLUDING INTRINSIC NATURAL SELECTION AND SEXUAL SELECTION AGAINST HYBRIDS

Maladaptive hybridization is hypothesized to be an important force driving the evolution of reproductive isolation between closely related species. Because the magnitude and direction of selection can vary across a life cycle, an accurate understanding of the ubiquity of reinforcement requires fitness to be estimated across the life cycle, but the literature is surprisingly depauperate of such studies. We present fitness estimates of laboratory‐raised hybrids between the chorus frogs Pseudacris feriarum and Pseudacris nigrita—two species that have undergone reproductive character displacement where they come into secondary contact. By studying viability, mating success, and fertility across the life cycle, we find strong support for reinforcement as the force driving displacement in this system. Specifically, we find hybrid fitness is reduced by 44%. This reduction results from both sexual selection against hybrid males and natural selection on male fertility, but not viability selection. Sexual selection against hybrid males is four times stronger than natural selection. Hybrid female fitness is not reduced, however, suggesting that Haldane's rule may be operating in this system if males are heterogametic. We also found higher variation in hybrid male fertilization success relative to P. feriarum males, suggesting that the hybrid incompatibility genes are polymorphic within one or both of the parent species.     

属鱼类的分类整理（鲤形目：鲤科）

本文对鲤科、亚科的属鱼类分类进行全面的整理和研究,除增补和作必要更动外,还描记二新种,间,新种Ｈｅｍｉｂａｒｂｕｓｍｅｄｉｕｓｓｐ．ｎｏｖ．和短鳍,新种Ｈｅｍｉｂａｒｂｕｓｂｒｅｖｉｐｅｎｎｕｓｓｐ．ｎｏｖ,重整后本属共计８种。     

鳅鮀属鱼类一新种

本文报道了鲤科鳅(鱼它)属鱼类一新种,定名为少耙鳅(鱼它)Gobiobotia paucirastella。和近似种裸胸鳅(鱼它)Gobiobotia tungi相比,该新种胸腹部裸露区较大,鳃耙与侧线鳞较少。     

FIRST FOSSIL EVIDENCE FOR THE PRIMITIVE ANGIOSPERM FAMILY LACTORIDACEAE

Pollen of the primitive angiosperm family Lactoridaceae has been recovered from Turonian-Campanian (Upper Cretaceous) sediments from eleven boreholes off the southwest coast of southern Africa. This is the first report of the Lactoridaceae in the fossil record. The one extant species of the Lactoridaceae is confined to the Juan Fernandez Islands located off the coast of Chile. The occurrence of lactoridaceous pollen in Cretaceous deposits of southern Africa suggest that this primitive angiosperm family may have been more widespread in the Southern hemisphere during the Cretaceous.     

SELECTION FOR NATIVE CHARACTERS IN HYBRIDS BETWEEN TWO LOCALLY ADAPTED PLANT SUBSPECIES

Gene exchange between locally adapted plant populations can have significant evolutionary consequences, including changes in genetic diversity, introduction of adaptive or maladaptive traits, disruptive of coadaptive gene complexes, and the creation of new ecotypes or even species. The potential for introgression between divergent populations will depend on the strength of selection against nonnative characters. Morphologically variable F₂ hybrids of two Gilia capitata subspecies were used to evaluate the strength of phenotypic selection and the response to selection in the home habitats of each subspecies. At both sites, traits diagnostic of the subspecies were subject to significant phenotypic selection, probably mediated by direct selection on unmeasured correlated characters. Phenotypic selection favored native morphologies in all but a single case; leaf shape of one subspecies was favored in both habitats. The strength of selection varied between sites, with one site selecting more strongly against nonnative characters. Offspring of the F₂ hybrids showed a significant evolutionary response to selection when grown in a common environment. Evolution was in the direction of similarity with the subspecies native to the site where selection was imposed. This result reveals that native character states are adaptive and suggests that selection will maintain native morphologies even after a substantial influx of genes from an ecologically and morphologically distinct, and locally adapted subspecies.     

中国缨鱼属鱼类的分类整理及一新属描述（鲤形目：鲤科）

经整理我国缨鱼属鱼类仅有１种,原属于此属的种Ｃｒｏｓｓｃｈｅｉｌｕｓ ｂａｍａｅｎｓｉｓ Ｆａｎｇ和Ｃｒｏｓｓｏｃｈｅｉｌｕｓ ｌｉｕｃｈｅｎｇｅｎｓｉｓ Ｌｉａｎｇ则归并于另一新属拟缨鱼属Ｐｓｅｕｄｏｃｒｏｓｓｏｃｈｅｉｌｕｓ ｇｅｎ．ｎｏｖ．,其上唇消失,吻皮与下唇相连,上颌与下唇相连以及口角须发达等特征与缨鱼属不同,同时其口角须发达,下唇两侧有纵行的颏汉以及下唇前缘具有显著的乳突状角质突起等