Asymmetrical reproductive character displacement in the house mouse

Our study addressed reproductive character displacement between two subspecies of the house mouse, Mus musculus musculus and Mus musculus domesticus that hybridize in Europe along a zone where selection against hybridization is known to occur. Based on a multi-population approach, we investigated spatial patterns of divergence of mate preference in the two taxa. Mate preference was significantly higher in the contact zone than in allopatry in both subspecies, suggesting that reproductive character displacement occurs. Moreover, patterns of preference were stronger in M. m. musculus than in M. m. domesticus, indicating an asymmetrical divergence between the two. In the context of selection against hybridization, our results may provide empirical support for the hypothesis of reinforcement in a parapatric hybrid zone. We discuss factors that could explain the asymmetrical pattern of divergence and the possible impact of a unimodal structure on the maintenance of premating divergence between the two subspecies.     

The reproductive ecology of Mohave rattlesnakes

The reproductive ecology of Mohave rattlesnakes Crotalus scutulatus was investigated in the western Mohave Desert using radiotelemetry from August 2001 to November 2004. This paper documents reproductive behavior across successive seasons in the context of seasonal timing, mean daily movement, home range, body temperature and relationship with abiotic factors such as time of day, temperature, precipitation, photoperiod and microhabitat. This population of C. scutulatus used a bimodal mating system, with reproductive behavior occurring in late summer/fall (21 August to 7 October), interrupted by 4 months of cold weather, and concluding in the spring (16 March to 16 May). Drought apparently curtailed courtship and copulation during the 2002 activity season, but the pregnancy rates in 2002 and 2003 were not significantly affected. Communal denning was not detected and there was no indication of seasonal migration. Autumnal and vernal movements appeared to be driven by reproductive effort, predominantly males engaged in prolonged mate searching. Sexual maturity was achieved at 2.0 years/600 mm snout–vent length (SVL) for females, and 1.5 years/400 mm SVL for males.     

The ecology and evolution of reproductive synchrony

The temporal pattern of breeding in populations is often characterized by a pronounced temporal clustering of births, flowering or seed set. It has long been suspected that this phenomenon is not caused by climatic seasonality alone but that reproductive synchrony represents a strategy that individuals adopt to maximize reproductive success. The classical hypotheses predicting an adaptive advantage of reproductive synchrony incorporate both sociobiological and ecological explanations. However, new theoretical and empirical analyses have shown that the predicted advantage of reproductive synchrony depends on the ecological setting in which populations reproduce, and processes earlier thought to be responsible only for synchrony may under some ecological conditions lead to asynchronous reproduction being the best strategy.     

Genetic variation in plasma prealbumin of the house mouse.

Rate of electrophoretic migration of prealbumin-2 of mouse blood plasma was found to be controlled by three autosomal codominant alleles. Presence and absence of a component next to albumin (prealbumin-4) was shown to be controlled by autosomal dominant and recessive alleles, respectively, and to be affected by sex. Evidence was presented for close linkage of the Pre-2 and Pre-4 loci, and for the control of albumin conformation by a separate locus.     

The non-random occurrence of Robertsonian fusion in the house mouse

Chromosomal rearrangements such as Robertsonian (Rb) fusions constitute a major phenomenon in the evolution of genome organization in a wide range of organisms. Although proximate mechanisms for the formation of Rb fusion are now well identified, the evolutionary forces that drive chromosomal evolution remain poorly understood. In the house mouse, numerous chromosomal races occur in nature, each defined by a unique combination of Rb fusions. Among the 106 different Rb fusions that were reported from natural populations, the low involvement of chromosome 19 in Rb fusions is striking, prompting the question of the randomness of chromosomal involvement in Rb fusions. We uncover a significant quadratic relationship between chromosome size and probability of fusing, which has never previously been in this species. It appears that fusions involving chromosome 19 are not particularly infrequent, given the expected low fusion probability associated with the chromosome's size. The results are discussed, assessing selective processes or constraints that may operate on chromosome size.     

Total sex-linkage in the house mouse

Summary 1. A totally sex-linked gene, Tabby (Ta), in the house mouse is described. It is semi-dominant in females. Mutant males resemble homozygous females, which shows that there is no homologue on the Y-chromosome.2. Heterozygous females have transverse black markings, visible only in agoutis. Homozygous females and hemizygous males have a number of defects exactly resembling those produced by the autosomal recessive crinkled.3. Brindled and Mottled are shown also to be totally sex-linked, by means of linkage tests with Tabby in doubly heterozygous females. Both Brindled and Mottled recombine with Tabby with a frequency of about 4%. This proves that crossing-over takes place in the differential segment of the X-chromosome in females.

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Zusammenfassung 1. Tabby (Ta) ist ein völlig geschlechtsgebundenes Gen in der Hausmaus. In Weibchen zeigt es unvollkommene Dominanz. Männchen mit dieser Mutante gleichen homozygoten Weibchen, ein Beweis, daß das Y-Chromosom kein homologes Gen enthält.2. Heterozygote Weibchen haben schwarze Querstreifen, die nur auf Agouti-Hintergrund erkennbar sind. Homozygote Weibchen und hemizygote Männchen zeigen eine Anzahl von Abnormitäten, die genau den von dem recessiven Autosomalfaktor crinkled hervorgerufenen gleichen.3. Brindled und Mottled sind gleichfalls völlig geschlechtsgebunden; das geht hervor aus Koppelungsversuchen mit Weibchen, die heterozygot für Tabby und eines dieser Gene sind. Sowohl Brindled und Mottled haben Tabby gegenüber eine Rekombinationshäufigkeit von ungefähr 4%. Das beweist das Vorkommen von crossing-over in dem Differentialsegment des X-Chromosoms in Weibchen.

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With 1 figure in the text.

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Agricultural Research Council Scientific Staff.     

The ecology and evolution of male reproductive behaviour in the bees and wasps

Males of aculeate Hymenoptera differ in the behavioural adaptations employed to locate and secure mates. The ecological and evolutionary bases of these differences are explored in this paper. Male bees and wasps search for females by patrolling widely within emergence-nesting areas or within patches of flowers attractive to conspecific females, or by waiting at landmarks, at specific emergence sites, or at nests. Nest dispersion, flower distribution, the type of female mating system and the nature of male-male competition appear to be key factors in determining the mate-locating behaviour of males. Of special interest in multiple-mating by females, which may be an evolutionary response to the costs of attempting to resist copulation in certain situations. When polyandry occurs, males are under selection pressure to be the last male to copulate with a female prior to oviposition if sperm precedence occurs. In species in which females mate just once, a selective premium is placed on being the first male to reach a virgin female. In either case, because receptive females are a limited resource, there is intense competition among males for access to the resource. The density of competitor males may play an important role in determining whether holding a relatively restricted territory is preferable to the strategy of patrolling widely at various sites which may have females. Territoriality is practiced by males of several species of aculeate Hymenoptera when the number of male competitors is relatively few in number and the distribution of emergence sites or foraging areas of females is clumped in space.     

The uncharacterized gene 1700093K21Rik and flanking regions are correlated with reproductive isolation in the house mouse,Mus musculus

Reproductive barriers exist between the house mouse subspecies, Mus musculus musculus and M. m. domesticus, members of the Mus musculus species complex, primarily as a result of hybrid male infertility, and a hybrid zone exists where their ranges intersect in Europe. Using single nucleotide polymorphisms (SNPs) diagnostic for the two taxa, the extent of introgression across the genome was previously compared in these hybrid populations. Sixty-nine of 1316 autosomal SNPs exhibited reduced introgression in two hybrid zone transects suggesting maladaptive interactions among certain loci. One of these markers is within a region on chromosome 11 that, in other studies, has been associated with hybrid male sterility of these subspecies. We assessed sequence variation in a 20 Mb region on chromosome 11 flanking this marker, and observed its inclusion within a roughly 150 kb stretch of DNA showing elevated sequence differentiation between the two subspecies. Four genes are associated with this genomic subregion, with two entirely encompassed. One of the two genes, the uncharacterized 1700093K21Rik gene, displays distinguishing features consistent with a potential role in reproductive isolation between these subspecies. Along with its expression specifically within spermatogenic cells, we present various sequence analyses that demonstrate a high rate of molecular evolution of this gene, as well as identify a subspecies amino acid variant resulting in a structural difference. Taken together, the data suggest a role for this gene in reproductive isolation.     

Centromeric heterochromatin polymorphism in the house mouse

Polymorphism of Giemsa-specific centromeric heterochromatin (C.H.) has been described in the laboratory and wild mice. All examined wild mice and inbred mouse strains display some chromosomes with considerably reduced or enlarged C.H. regions. The quantity of C.H. could be an inherent property of a chromosome as inferred from (a) the finding of the identical C.H. pattern within inbred strains, (b) the finding that two genetically related inbred strains, C3H and CBA, separated from each other for more than 150 generations, possess the same two chromosome pairs with tiny C.H. marker regions. These chromosomes were identified as No. 1 (l.g. XIII) and No. 14 (l.g.III) by means of T(14;15)6Ca translocation, and C- and G-band analysis. The neutrality of C.H. polymorphism in murine genome is inferred from the heterozygosity for the C.H. variants found in all studied wild mice. The possible relationship of C.H. polymorphism to the centromere interference phenomenon is hypothesized.     

植物繁殖生态学的若干重要问题

发现模式,并根据过程解释模式,是科学研究的主要目标.在植物繁殖生态学领域内,人们已经总结了一些重要的模式,包括普遍的雌雄同体、分离的花果期、较低的结实率、大量的同时开花、胁迫生境更易出现的异交、生活史性状与交配系统的相互作用、花序内的花分化,以及花内的雄蕊分化(异型雄蕊)等.对这些模式如何从机理上予以解释,还需要植物繁殖生态学家的艰苦努力.本文着重强调了植物许多重要繁殖特征都可以通过植株、花序以及花各层次上的资源分配而得到很好的解释,尤其是可以在很大程度上协调其他不同侧重点研究得到的矛盾结论.在今后逐渐强调多因素、多尺度对花部特征与传粉系统的适应与进化的研究中,从直接决定花部特征与交配系统的资源分配出发,将是促进人们准确理解与预测花部特征适应与进化的一个重要研究方向.     

Studies on salmonellosis in the house mouse, Mus musculus.

Salmonellae were isolated from the faeces from 17 of 170 (10%) wild house mice. Salmonella typhimurium was isolated from 10, S. typhimurium, var. Copenhagen from 2, S. thompson from 1, and S. muenchen from 4. It was concluded that house mice could be a reservoir of infection and play an important role in human and animal salmonellosis.