Female mate choice and species recognition between two closely related cichlid fish of Lake Malawi,Metriaclima estherae and M. callainos

Cichlids are one of the most diverse and colourful groups of freshwater fishes in the world. Despite much investigation, the factors that promote speciation in these fishes are still uncertain. However, previous studies suggest that sexual selection on male colour is one of the main drivers of speciation among these fishes. Metriaclima estherae is a polymorphic cichlid species from Lake Malawi, and thus provides an ideal model for the investigation of the importance of colour as a species recognition cue. M. callainos is a closely related and morphologically similar species, with male colour pattern very similar to that of M. estherae. We tested female choice by giving females of the two species a choice between conspecific and heterospecific males in the presence and absence of visual (colour) and chemical cues. The results show that females of M. callainos were able to reliably recognize conspecific males, even when colour was eliminated as a cue. However, females of M. estherae did not prefer conspecific males, although they were able to discriminate between red and blue conspecific colour morphs by using chemical cues. These results suggest that species recognition cues may differ even among closely related species of cichlid fish, and that female preferences for male coloration may be weak in certain species.     

A STUDY OF A FIELD POPULATION OF THE BLOWFLIES LU CILIA CAESAR (L.) AND L. SERICATA (MG.)

Attempts to measure the dispersion, population density and longevity of blowflies are described. The experiments were made at Aber, Caernarvonshire, in 1943 on a narrow strip of coastal farm land (if x f ml.). Two liberations of laboratory-bred Lucilia sericata (Mg.) were made. On the second occasion 286 flies of each sex were marked, and nine males and nineteen females were captured, the last capture occurring 15 days after liberation. The population density of this species was estimated to be approximately seven males and sixteen females per acre for the 840-acre strip on the day of the second liberation.
On 24 days during the period 20 August–20 September 1943, field-caught L. caesar (L.) females were marked, and trapping both by meat and chemical baits was continued for a further 3 weeks. 3600 females were marked, 847 being recaptured at least once, and sixteen on at least four occasions. In the later part of the blowfly season, a life of 5–6 weeks is apparently not unusual for L. caesar females. The population drawn upon by the traps at the liberation centre fluctuated between 700 and 30,000 during the 4-week period. This may have represented a very localized concentration equivalent to 6–238 females per acre. Dispersion of marked L. caesar was low. On the assumption of a maximum spread of 5 miles, some 63 % of the marked flies remained within 4 mile of the liberation centre.     

Ontogenic colour change,survival, and mating in the damselfly Agriocnemis pygmaea Rambur (Insecta: Odonata)

1. Damselflies often show intra-specific colour variation, which may represent genetic polymorphism or age-related (ontogenic) colour changes. 2. Such variation has distinct implications for the species' ecology and evolution. Colour variation in females of the damselfly Agriocnemis pygmaea was studied, which range from blue male-like individuals (andromorphs) to those with a distinct red colour (heteromorphs). From preliminary observations, it was hypothesised that this species exhibits ontogenic colour change from heteromorph to andromorph coloration. 3. Mark–recapture experiments and egg counts of dissected females suggested that immature females are heteromorphic and gradually begin to resemble males as they attain sexual maturity. 4. Reflectance spectra of field-caught individuals indicated that, although males are indistinguishable from andromorphs, they could be easily differentiated from heteromorphs. 5. Finally, field observations and mate choice experiments showed that males rarely attempt to mate with heteromorphic females and prefer andromorphs. Together, this study's results suggest that the observed colour variation in A. pygmaea females is ontogenic and is associated with sexual maturity.     

Morphometric discrimination of the sibling species Drosophila melanogaster (Meigen) and D. simulans (Sturtevant) (Diptera: Drosophilidae)

Abstract. The sibling species Drosophila melanogaster and D.simulans often co-occur. Males are easily distinguished using their genitalia while females of the two species are often deemed indistinguishable. A series of nine linear and two angular measurements were taken using the heads of both males and females of both species from the same locality. A simple comparison of cheek width and eye height accurately assigned all females to species. Multivariate techniques using linear head measures alone produced very good discrimination between both species and sexes. Drosophila simulans have significantly larger eyes and narrower eye margins than D.melanogaster. Unknown females collected from this locality could be easily and reliably assigned to species.     

Spectral data reveal unexpected cryptic colour polymorphism in female sailfin silverside fish from ancient Lake Matano

Persistent colour polymorphisms can result from natural and/or sexual selection, and may occur in males, females, or both sexes. Contrary to conspicuous patterns frequently observed in courtship colouration, differences in cryptic colouration are not always perceived by the human sensory system. In sexually dimorphic sailfin silversides fishes, males show conspicuous colour polymorphisms whereas females appear monomorphic and cryptic. We measured the spectral composition of body, fin and peduncle colouration in male and female Telmatherina antoniae ‘small’, a sailfin silverside species endemic to ancient Lake Matano, and found evidence for a colour polymorphism in both sexes. The three colour morphs distinguished by spectral data correspond to those commonly reported for males, and are also present in the visually (to a human eye) cryptic females. Females show hue value patterns similar to those present in males, but differ from males substantially in chroma and brightness. This is, to the best of our knowledge, the first example of a cryptic colour polymorphism in fishes; however, its significance for the mating system remains unknown. The present finding highlights the need for incorporating female spectral data into analyses of colour patterns, and suggests that colour analyses should include cryptic sexes.     

Genetics of the butterfly Danaus chrysippus (L.) in a broad hybrid zone, with special reference to sex ratio, polymorphism and intragenomic conflict

The aposematic savanna butterfly Danaus chrysippus seems to be an exception to the rule that Batesian models and Müllerian mimics are not polymorphic. Throughout Asia and in much of Africa the species is in fact monomorphic and polytypic, as expected. It is, however, polymorphic for 3–4 colour genes over a large area of central and eastern Africa, where deviant sex ratios and non-Mendelian segregations also occur. All-female broods are widespread and frequent, often outnumbering bisexual progenies and giving rise to heavily female-biased populations. Full and partial sex linkage, which is not controlled from the X or Y chromosomes, and male-biased broods also occur. Genetical analysis for the BC-autosome carrying colour genes suggests there are two, probably mitochondrial, cytotypes (microbe-induced early male death syndrome is considered unlikely) and an autosomal, incompatibility (I) gene, two alleles of which are male-specific killers. F2 and backcross matings by females heterozygous at the 1-locus give progenies which are either thelygenic, all males dying at or soon after hatching, or bisexual but showing full or partial sex linkage. Male death is attributed to nuclear-cytoplasmic incompatibility (NCI). Females achieve reversion from a thelygenic to a bisexual line by mating with males of compatible (maternal) cytotype. A second NCI system causes meiotic drive in female oögenesis for a cytoplasmically compatible A-autosome, with no effect on SR. The array of non-Mendelian segregations for sex and two autosomes, with switching between bisexual and unisexual lineages, indicates autosomal intragenomic conflict with the outcome that one autosome is preserved from elimination in females and the other condemned in dead males. The geographical distribution of the colour marker genes suggests that the polymorphisms have a hybrid origin involving several once allopatric subspecies, some of which have divergent cytotypes. Secondary contact probably followed range expansion induced by the periodic spread of savanna during the Pleistocene and massive deforestation by man in recent times. The unusual extent of the hybrid zone is attributed to the large number of subspecies involved in its origin, and to introgression promoted by the butterfly's extensive migratory activity.     

Genetic difference in female choice between two guppy populations

The pattern of mating preferences of female guppies, Poecilia reticulata, differs genetically between two Trinidadian populations. Males from the Aripo and Paria rivers of Trinidad differ in the extent and intensity of orange pigment in their colour patterns. The relative area of orange in Paria colour patterns was nearly twice that in Aripo colour patterns. To test the hypothesis that a difference in female mating preferences could have contributed to the difference in colour patterns, patterns of female choice between laboratory-reared Paria and Aripo females were compared. The frequency of sexual responses to male courtship displays was used to measure the average preference of females for individual males. Paria females discriminated significantly between Paria males based upon differences in the extent of orange in the colour pattern. Aripo females showed no evidence of discrimination between Paria males, and thus differed significantly from Paria females in choice behaviour. Neither group of females discriminated between Aripo males. These results are evidence that female choice behaviour can vary genetically within a species and suggest that differences in preferences may have contributed to divergence in colour patterns among guppy populations.     

Postembryonic development of the spider Enoplognatha ovata (Clerck) (Araneae:Theridiidae)

The postembryonic development of the three colour varieties of Enoplognatha ovata (CI.) was studied in the field and in the laboratory for two generations. Native and European spiders of this species were compared. Estimates of the number and duration of each stage were obtained from laboratory mating studies and verified by field studies. Males and females matured after five instars. Males matured faster than females but did not live as long. Each instar was characterized by several measurable parameters. All varieties over-winter in the second instar. Sexes could be easily separated at the fourth instar by comparing the ratio of the tarsal to patellar width of the pedipalps. Sexual dimorphism occurs at maturation ecdysis. Filial and mating studies indicate that the three colour varieties belong to a single species.     

Resurrection of Aedes (Halaedes) ashworthi Edwards 1921: Morphological Characterisation and Separation from its Sibling Aedes (Halaedes) australis (Erichson) 1842 (Diptera: Culicidae)

The result of population crosses of members of the Ae. australis complex and the examination of the male genitalia of these populations have shown that Ae. ashworthi Edwards 1921 should be reinstated as a valid species. the parent females laid viable eggs when cross mated to males of different species, but the resulting F₁ females and males were largely sterile. When F₁ females were blood-fed and examined 3–8 d later, usually fewer than 10 ovarioles per ovary developed recognisable follicles and none of these formed eggs. F₁ males in nearly all cases possessed half-size testes, and there was no spermatid development in the reduced testes. A few males had normal-sized testes, but the spermatids were mostly tailless. the male of Ae. ashworthi can be separated from Ae. australis by the shape of the gonocoxite and the length of the gonostylus of the genitalia. the larvae of both species are identical, and the females differ only in the colour of some scale patches and the integument, which may prove to be too variable to be useful when more populations are compared. the morphological similarity of the two mosquitoes as larvae and adults supports the proposal that they should be recognised as sibling species, with Ae. ashworthi as the derived member of the Ae. australis complex. It is clear from morphological evidence, the viability of the F₁ hybrids and the unusual habitat occupied by both species, that they have diverged recently.     

Seasonal and spatial changes in blowfly production from small and large carcasses at Durham in lowland northeast England

Colonization by blowflies (Diptera: Calliphoridae) of mouse carcasses exposed in open agricultural land near Durham (54 45'N) changed from early spring monopolization by Calliphora vicina R.-D. to a summer pattern of multiple species exploitation by this species together with Lucilia caesar L., L. illustris Mg., L. silvarum Mg., L. sericata Mg. and L. richardsi Collin. In a garden at the edge of Durham, mouse carcasses were dominated by C. vicina from spring to autumn. Difference in mouse colonization between the agricultural and garden sites seemed to reflect differences in the blowfly species present, as measured by baited trap catches at the sites. In sets of C. vicina reared from mice under conditions of competition for larval food, it was found that resulting females were significantly larger than males, size being measured as mean wing length. Blowfly production from three sheep carcasses exposed successively at the agricultural site was dominated by C. vomitoria L. and L. caesar, but also produced other Lucilia species in small numbers, including L. sericata. These L. sericata females from sheep that had died from causes other than myiasis included full-sized specimens, in contrast to those produced from mouse carcasses that were all undersized individuals. As L. sericata females trapped on sheep pastures are predominantly full-sized, this suggests that large carcasses may, in part, be a source of the L. sericata population that attacks sheep as a myiasis agent. The nature of large carcasses as possible sources of L. sericata in lowland Britain is discussed.     

Tryptophan, copper and zinc in hair of healthy subjects. Correlation with differences in hair pigmentation

Tryptophan, copper and zinc levels were determined in the hair of 300 healthy subjects divided by sex, age and hair colour. Sex influences tryptophan content in hair, the levels of this amino acid being higher in males than in females. Tryptophan is also higher in infancy (2-5 years) and in both males and females aging around 80 years and over. Hair colour also influences tryptophan levels, which increase from fair to black hair. Copper levels are similar in hair of both males and females, while those of zinc are higher in women. Age influences the distribution of these two metals in human hair. Copper contents in hair of males are higher at the age 20-40 years. In females, values decrease over the age of 60 years. Instead, zinc levels are higher between 20 and 60 years in males, and between 13 and 19 years in females. As regards hair colour, copper is slightly higher in black hair in males and in fair hair in females, and lower in white hair in both sexes. Zinc values appear to be higher in red and lower in white hair in males. In females they are higher in black hair.     

Female Colour Polymorphism: Gender and the Eye of the Beholder in Damselflies

Damselflies provide a classic example of female colour polymorphism. Usually, one female morph resembles the blue male colour (andromorph) while one, or more, female morphs are seen as typically female (gynomorph). Damselfly species fall in two distinct groups with respect to recent developments in mimicry theory: in some species females are perfect, they match male colouration and black patterning, and in other species they are supposed to be imperfect mimics, only matching male colouration. However, the underlying assumption of one female morph looking male-like is mostly based on human vision. Therefore we investigated the black patterning and colour of the three female morphs in Coenagrion puella, an imperfect mimic, using image analysis. In C. puella the blue female morph is perceived as male-like. We found that the black patterning of such females cannot be distinguished from the other female morphs, and is clearly different from males. Furthermore, the blue colour of andromorph females differs from the blue colour of males. Intriguingly, however, the red content did not differ between blue males and females.     

Pheromonal Recognition of Females Takes Precedence over the Chromatic Cue in Male Iberian Wall Lizards Podarcis hispanica

Sex recognition is based on colour signals in many species of lizards. However, olfactory stimuli are also clearly involved, and many species might rely more on chemoreception. We aimed to examine whether colour pattern or odours, or both, are used in sex recognition and which cues elicit courtship of females by males of the lizard Podarcis hispanica . We experimentally manipulated the coloration and odour of female P. hispanica , thereby creating groups with all combinations between coloration and odour of males and females. Using data from staged encounters, we compared the responses of resident males to manipulated and unmanipulated individuals (males and females). Responding males reacted significantly more aggressively to female intruders with male odours, independently of their coloration. Nevertheless, coloration seemed to be important in long-distance sex recognition since, in the first minutes, females painted as females received a lower number of aggressive responses. Both colour and odour were important in eliciting male courtship. However, females painted as females and with female odours were preferentially courted. Comparisons with unmanipulated male and female intruders agreed with these expectations. Therefore, at close range, odoriferous cues seem to be more important than colour patterns in sex recognition, but female coloration is also useful at long range to deter the aggressive response of males and to elicit courtship in conjunction with odours.     

Phenology of two territorial solitary bees, Anthidium manicatum and A. florentinum (Hymenoptera: Megachilidae)

Five years' data on phenology of an Anthidium manicatum population in southern Germany and comparative observations on A. manicatum and A. florentinum from southern France are analysed. Males and females had the same flight season, adult sex ratio was strongly female biased and males were larger than females in both species. This is the opposite pattern to most other solitary bees, where females generally are larger than males, sex ratio is male-biased, males emerge before females and males disappear long before females. We argue that two features of Anthidium female behaviour, namely prolonged sexual receptivity and use of resources easily defendable by males, explain male adaptations in behaviour, phenology and body size and, hence, population sex ratio.     

Unusual sex roles in a highly promiscuous parrot: the Greater Vasa Parrot Caracopsis vasa

We describe the unusual mating system of the Greater Vasa Parrot Caracopsis vasa . The dull black plumage of males and females is similar but females are significantly larger than males. Females are promiscuous and copulated with at least five different males. Copulations were either short (1–3 s) or very long (mean 35.9 min), and long copulations involved a copulatory tie facilitated by the male's enlarged cloacal protrusion. Multilocus DNA fingerprinting of 17 broods showed that all were of mixed paternity, and that some broods had three fathers. Males never visited nests directly, but during the incubation and chick-rearing periods females came off the nest and were fed regurgitated fruit by multiple males. Four had band-sharing coefficients that suggested they were unrelated. Males copulated with and provided food for several widely separated females simultaneously. During the chick-rearing period females defended a territory around the nest from conspecific females, developed conspicuous orange skin on the head (through feather loss), and uttered loud, complex vocalizations that we refer to as 'song' from prominent perches near the nest. Males showed none of these traits. Females with high song rates attracted more males and as a result received more food than other females. Play-back experiments in which female song rates were either increased or decreased, attracted more or fewer males respectively. We propose that female song, conspicuous head colour and territoriality have all evolved as a result of competition between females for the food provided by males. The selective pressures favouring this highly unusual breeding system in the Greater Vasa Parrot are unclear but some sort of ecological constraint, such as food availability, may be important.     

Does character displacement demonstrate density-dependent expression in females? A test on the wing shape of two species of European damselflies

Character displacement (CD) is the evolutionary process which leads to the divergence in trait expression of closely related species in regions where species co-occur, compared to allopatric populations. In Europe CD has been investigated in males of Calopteryx splendens and C. virgo and has been related to species recognition. If species recognition is relevant for males, also females should benefit from CD. The most obvious differences between females of these two species are wing profile and colour. We sampled females from allopatric and from sympatric populations with different relative abundances of these species. Wing shape and pigmentation were evaluated for each damselfly. CD was found in wing profile but not in wing transparency. The relative abundance of species significantly affected CD, but with a different pattern in each species. The prediction that wing shape become more different from the allopatric state when the species was relatively rare, but more similar to the allopatric state when the species was common was evident only for C. splendens. Wing shape changes might increase differences in flying patterns making males more effective to discriminate between heterospecific females. So, CD we observed may be the result of a selection directed to reduce interspecific reproductive interference.     

Socially transmitted mate preferences in a monogamous bird: a non-genetic mechanism of sexual selection

There is increasing evidence that animals can acquire mate preferences through the use of public information, notably by observing (and copying) the mate preferences of others in the population. If females acquire preferences through social mechanisms, sexual selection could act very rapidly to spread the preference and drive elaboration of the preferred trait(s). Although there are reports of 'mate-choice copying' in polygynous species, there is no clear evidence for this process in monogamous species. Here, we investigated whether adult female zebra finches Taeniopygia guttata can socially acquire sexual preferences for individual males and, in a separate study, for a generalized trait (coloured leg bands) of males. In both studies, test females observed males in two simultaneous conditions: a ('chosen') mixed-sex situation in which a male was paired with a (model) female, and a ('unchosen') same-sex situation in which a male was paired with another male. In the first experiment, after two weeks of females observing males, test females significantly preferred individual males who had been paired with another female (i.e. chosen males). In the second experiment, test females significantly preferred novel males that were wearing the same leg band colour as the apparently chosen males. Our findings are consistent with the conclusion that female zebra finches' mate preferences are altered by public information. Our study implies that mate preferences can spread rapidly through populations by social mechanisms, affecting the strength of sexual selection in a monogamous species.     

Geographic distribution of human skin colour: A selective compromise between natural selection and sexual selection?

Modern humans have been shaped by the cumulative action of natural selection, non-adaptive random change, and sexual selection. The last of these is not universal and has prevailed in one of two circumstances: (1) A surplus of females due to high male mortality, combined with ecological constraints on female participation in food procurement which discourage males from taking second wives; (2) A surplus of single males due to generalized polygyny with relatively low male mortality. These circumstances are most likely to occur in (1) Arctic tundra environments, specifically the vast expanse of tundra covering most of Europe up to 10,000 B.P., and in (2) regions dominated by generalized polygyny, notably sub-Saharan Africa. Sexual selection often acts on existing sex differences, including perhaps sexual dimorphism in human skin colour. Whereas women are universally fairer in complexion, men are browner and ruddier; parallel to this, most human societies see lighter skin as more feminine and darker skin as more masculine. Hence, sexual selection should favour lighter pigmented women when a surplus of single females must compete for a mate. Since skin colour is only mildly sex-linked, both sexes would lighten in pigmentation within the population in question. Similarly, when a surplus of single males must compete for a mate, both sexes would darken. Geographic variation in human skin colour may thus represent a selective compromise between two counterbalancing forces: natural selection, as determined by latitudinal variation in sunlight; and sexual selection, as determined by variations in the following: male mortality rates, incidence of polygyny, and ecological constraints on female participation in food procurement.     

Colouration in Atlantic puffins and blacklegged kittiwakes: monochromatism and links to body condition in both sexes

Sexual dimorphism is widely used as an indirect measure of the intensity of sexual selection. It is also a way to evaluate whether different selective pressures act on males and females. Dichromatism, defined as a difference in colouration between males and females, may for instance result from selection for crypsis in females and selection for conspicuousness in males. Here, we conducted a study to investigate whether differential sexual selective pressures might act on the colour traits of two colonial seabird species, the Atlantic puffin Fratercula artica and the black‐legged kittiwake Rissa tricactyla. First, we used spectrophotometry and visual modelling to determine whether these presumed monomorphic birds are really monochromatic from an avian perspective (birds and humans have a different vision). Second, we estimated whether some of their colourations have the potential to be sexually or socially selected by determining whether these colourations were related to body condition in males and females, and whether the yellow, orange and red colourations may contain carotenoid pigments. Our results indicated that both species were fully monochromatic from an avian perspective. Moreover, our preliminary analyses suggested that the yellow, orange and red colours of these birds contained carotenoids. Lastly, some indices of colouration were positively linked to estimates of condition. Birds in better condition had redder gape (both species) and bill (puffins). In puffins, the relation between condition and gape colouration was significantly stronger in females than males. By contrast, the size of the gape rosette was larger in males than females. The positive links we found between colour indices and condition, together with the absence of sexual dichromatism, suggest that mutual sexual selection may act in these two species.     

Body coloration and colour alternation among tropical forest mammals

Despite different phylogenetic origins, the mammals of Gabon and Guiana show very similar colour patterns. The coloration is closely correlated with several biological parameters: body weight, diet, and activity rhythm. The less dangerous the living conditions, the more easily perceptible are body colours. Within the same community, the degree of colour convergence between species of similar body size is very low among diurnal carnivores or between they and their prey, that is when interspecific encounters can be dangerous. In contrast, it is higher among diurnal terrestrial frugivores or folivores of similar size, than among those of unequal size. Owing to the few colours available, and to the regular size spacing between species, all species are arranged into narrow unicoloured size strata (indistinct colour or red), regularly alternating along the whole size range. Since most species of similar size are well differentiated from each other by ecology, each solitary animal can be sure that another having both the same size and colour is conspecific. The colour alternation does not exist when it is not useful: nocturnal, arboreal, or flying mammals.