Evolutionary Assurance vs. Mixed Mating

Reproductive assurance is a widely accepted explanation for the evolution of selfing, although theory suggests that an evolutionarily stable mixed mating strategy does not maximize seed production. We present a correlation analysis involving 28 species representing 23 families showing that selfing can evolve independently of inbreeding depression. We discuss the cost-benefit trade-off of selfing, in particular the incongruence of whether delayed selfing provides reproductive assurance in 22 species representing 14 families, in which pollen and seed discounting are minimized when pollinators or mates are scarce. Reproductive assurance, in response to frequent pollinator failure, can be reconciled with an evolutionarily stable mixed mating system contributed to by delayed selfing, which is still advantageous even if there is strong inbreeding depression.     

Mating aggregates in Escherichia coli conjugation.

Mating mixtures of Escherichia coli cells were shown to contain mating aggregates of two to 20 cells each rather than only mating pairs of two cells each. The mating aggregate size distribution shows two broad peaks, at two to four cells and at eight to 13 cells. The quantitative mating aggregate size distribution and the proportion of male cells in mating aggregates are dependent on the input ratio of male to female cells. At an input ratio of one to one, the average mating aggregate contains equal proportions of male and female cells and most of the cells involved in mating are in large aggregates of seven or more cells each. The deoxyribonucleic acid (DNA) transfer efficiency per mating aggregate cell was constant regardless of average aggregate size or of the ratio of male to female cells in the aggregate. Under optimal conditions essentially every male cell or every female cell in a mating aggregate can be involved in DNA transfer. A comparison of light microscopy, sucrose gradient centrifugation, and analysis with a modified Coulter counter indicated that the number of cells in mating aggregates is best equantitated using a modified Coulter counter.     

Assortative Mating

Abstract

Theories of mate selection and the effects of assortative mating are reviewed, including differences in the basic theoretical orientations of the social and biological sciences with respect to human evolution and assortative mating. Topics discussed include evolution in parallel and interaction, terminology of nonrandom mate selection, theories of mate choice, social stratification and class endogamy, and suggestions for future research.     

Mating Damages the Cuticle of C. elegans Hermaphrodites

Lifespan costs to reproduction are common across multiple species, and such costs could potentially arise through a number of mechanisms. In the nematode Caenorhabditis elegans, it has been suggested that part of the lifespan cost to hermaphrodites from mating results from physical damage owing to the act of copulation itself. Here, we examine whether mating damages the surface of the hermaphrodite cuticle via scanning electron microscopy. It is found that mated hermaphrodites suffered delamination of cuticle layers surrounding the vulva, and that the incidence of such damage depends on genetic background. Unmated hermaphrodites demonstrated almost no such damage, even when cultured in soil with potentially abrasive particles. Thus, a consequence of mating for C. elegans hermaphrodites is physical cuticle damage. These experiments did not assess the consequences of cuticle damage for lifespan, and the biological significance of this damage remains unclear. We further discuss our results within the context of recent studies linking the lifespan cost to mating in C. elegans hermaphrodites to male secretions.     

Mating and behavioural diapause inIxodes ricinus L.

This study established that in an open rough-grazing habitat in Ireland a large proportion of female ticks mated in the vegetation rather than on the host, confirming observations made by other workers in scrub and forest habitats in Switzerland and Russia. It was found that many ticks active from October onwards had already mated even though they were moulted and apparently derived from the spring population. This activity was at odds with theview that such ticks are prevented from becoming active in autumn by a behavioural diapause. Laboratory and plot experiments involving observations on questing activity and feeding showed that the behavioural diapause of females was abolished by exposure to males. Male ticks did not show a behavioural diapause. In areas of high tick density this mechanism could result in the transfer of ticks from spring to autumn populations and, since the mortality rate of the autumn population is higher, could also contribute to density-dependent population regulation.     

3种披碱草属牧草交配系统研究

本文通过测定3种披碱草属牧草的花粉-胚珠比（P/O值）、杂交指数（OCI）,结合不同授粉方式下这3种牧草的结实率,探讨这3种披碱草属牧草的交配系统, 为披碱草属牧草杂交育种、丰产栽培等提供理论依据。结果表明,老芒麦、麦薲草和披碱草花粉-胚珠比（P/O值）均处于31.9～396.0,交配系统属于兼性自交;杂交指数OCI值为2,交配系统也属于兼性自交;结实率统计表明,以自交为主,异交可育。因此,3种披碱草属牧草的交配系统属于兼性自交类型。     

Interconversion of Yeast Mating Types II. Restoration of Mating Ability to Sterile Mutants in Homothallic and Heterothallic Strains

The two mating types of the yeast Saccharomyces cerevisiae can be interconverted in both homothallic and heterothallic strains. Previous work indicates that all yeast cells contain the information to be both a and α and that the HO gene (in homothallic strains) promotes a change in mating type by causing a change at the mating type locus itself. In both heterothallic and homothallic strains, a defective α mating type locus can be converted to a functional a locus and subsequently to a functional α locus. In contrast, action of the HO gene does not restore mating ability to a strain defective in another gene for mating which is not at the mating type locus. These observations indicate that a yeast cell contains an additional copy (or copies) of α information, and lead to the "cassette" model for mating type interconversion. In this model, HMa and hmα loci are blocs of unexpressed α regulatory information, and HMα and hma loci are blocs of unexpressed a regulatory information. These blocs are silent because they lack an essential site for expression, and become active upon insertion of this information (or a copy of the information) into the mating type locus by action of the HO gene.     

Female Fitness Optimum at Intermediate Mating Rates under Traumatic Mating

Traumatic mating behaviors often bear signatures of sexual conflict and are then typically considered a male strategy to circumvent female choice mechanisms. In an extravagant mating ritual, the hermaphroditic sea slug Siphopteron quadrispinosum pierces the integument of their mating partners with a syringe-like penile stylet that injects prostate fluids. Traumatic injection is followed by the insertion of a spiny penis into the partner's gonopore to transfer sperm. Despite traumatic mating, field mating rates exceed those required for female fertilization insurance, possibly because costs imposed on females are balanced by direct or indirect benefits of multiple sperm receipt. To test this idea, we exposed animals to a relevant range of mating opportunity regimes and assessed the effects on mating behavior and proxies of female fitness. We find penis intromission duration to decrease with mating rates, and a female fecundity maximum at intermediate mating rates. The latter finding indicates that benefits beyond fertilization insurance can make higher mating rates also beneficial from a female perspective in this traumatically mating species.     

动物的婚配制度

婚配制度是动物种群个体为获得配偶普遍采取的一种行为策略。一般分为单配制、一雄多雌制、一雌多雄制和混交制。作为动物的一种进化稳定对策,婚配制度又具有一定的可塑性,有时可以逆转,有时又是兼性的。配偶外交配主要存在于单配制物种中特别是单配制鸟类中。其发现表明通过观察个体间联系来确定的“社会性婚配制度”和通过个体实际上的交配对象来描述的“遗传性婚配制度”有可能存在差异。婚配制度影响有害动物的不育控制,在存在繁殖性竞争的情况下,对单配制和一雄多雌制而言,不育效果最佳。     

Mating behaviour and fertility in domestic chickens. I. Inbreeding

Mating behaviour of males and females of the Inbred line 420 Single Comb White Leghorn chickens was compared with that of the random-bred Minnesota Marker line in a factorial experiment with two replications. Inbred males showed less frequency of approaching females, waltzing, treading and tail-bending, but did not differ from random-bred males in frequency of attempted and successful mountings. Inbred females showed fewer crouchings and completed fewer matings than random-bred females. Fertility was associated with the interaction of male and female behaviour.     

Response to Selection Under Non-Random Mating II. Prediction

A general expression for response to selection appropriate for both random and non-random mating situations is derived and illustrated with full-sibbing.     

Mating induces puberty in the female musk shrew.

Female musk shrews (Suncus murinus), lacking a behavioral estrous cycle, engage in copulatory behavior whenever tested; even during pregnancy, sexual activity can be displayed. Studies suggest that protracted sexual behavior has a functional significance in this species. Virgin females receiving a series of ejaculations over the course of several days are more likely to ovulate and subsequently deliver than animals given the same number of ejaculations over an interval of a few hours. After the virgin mating only one third of the ovaries placed in culture exhibit increased steroidogenesis. In the present set of studies, the hypothesis that the virgin mating induces the onset of puberty, in a manner similar to that in which male-related pheromones induce estrous in rodents, was tested. On the basis of gestational lengths it is evident that females mated three times (on Days 0, 4, and 8) became pregnant in the vast majority of cases as a result of the second and third matings. When the first and second matings were separated by 25 days, 82% of females ovulated in response to the second mating; less than one third of females mated only once ovulated. Finally females were housed across a screen from males, exposed to male urine, or housed alone prior to the virgin mating. In none of these cases did pre-exposure to male-related cues increase ovulation rates in response to the virgin mating. The results show that the virgin mating primes the neuroendocrine system in such a way that the pubertal ovulation can occur in response to subsequent mating.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mating in the mosquito, Anopheles gambiae s.l.

ABSTRACT. Swarming behaviour in the Anopheles gambiae complex was observed in the field, in the Gambia, West Africa, and in the laboratory. Naturally occurring swarms of A.melas were seen in a clearing at the edge of mangrove swamps close to their breeding sites. Males could be induced to swarm over artificial 'markers' within this 'arena' but not outside it. Females were observed entering the swarm and mating. In the laboratory, in an artificial 'dusk', male A.gambiae s.str. swarmed over a black marker on the floor of their 1.2-m cube cage. In contrast to the males, females made only short flights over the marker, performing brief turning movements at its edge. It is proposed that swarming brings about the aggregation necessary before short-range attraction can take place, and that, in nature, anopheline mosquitoes orientate visually first to an arena and then to a marker within the arena. Female behaviour can be interpreted as a process of scanning possible swarm sites until mating is achieved.