Mainland Females Research Articles

Contrasting Phenotypic Variability of Life-History Traits of Two Feral Populations of Macrolophus pygmaeus (Hemiptera: Miridae) under Two Alternative Diets

Tuta absoluta is a major pest attacking tomato crops. This invasive species emerged in Europe (Spain) in 2006, and 3 years later it spread to Portugal. In 2009/2010, it was recorded for the first time in the Azores archipelago. Macrolophus pygmaeus is a predator widely used as biological control agent against the tomato leaf miner. This study contrasted the life-history traits and population growth parameters of two feral populations of M. pygmaeus, one from Portugal mainland and one from the Azores archipelago. The predators were tested on single prey diet, either of Ephestia kuehniella eggs, a factitious prey used for mass rearing of mirids, or T. absoluta eggs. We predicted that populations would express differences in its phenotypic characteristics, with the Azorean population displaying low performance due to likely low genetic diversity, as expected for insular populations. Our results revealed the inexistence of phenotypic differences in several life history traits, such as immature developmental time, female longevity, males’ body weight and sex ratio. Contrary to our predictions, traits with direct impact on fitness, such as lifetime fertility (95.78 ± 14.23 vs. 61.38 ± 13.52 nymphs), explain better performances for the population of the Azores. Azorean M. pygmaeus females were larger, matured earlier and reproduced at a higher rate for longer periods, than mainland females. Therefore, population growth parameters show a positive advantage for the population of the Azores, fed on T. absoluta (time required for doubling the population Azores, Ek: 8.42 ± 0.50, Ta: 5.76 ± 0.31 and mainland, Ek: 10.88 ± 1.94, Ta: 12.07 ± 3.15). Biological performance of M. pygmaeus was similar when fed with T. absoluta or E. kuehniella that could be beneficial both to optimize mass production of the predator and biological control of the pest. Our results are discussed as well in a fundamental perspective, seeking if differences in biological performance can be explained by lower genetic diversity driven by geographic isolation.

Sex‐specific shifts in morphology and diet in a frog after 50 years of anthropogenic habitat fragmentation

AbstractAimPhenotypic shifts are commonly observed when animals face insular habitat change and may reflect ongoing stresses on individuals. However, the generality and the driving processes of this ‘island rule’ remain equivocal, notably in amphibians. Here, we investigate both morphological and dietary shifts in a frog using a mosaic of human‐created islands to assess the potential operating mechanisms underlying these phenotypic responses.LocationThousand Island Lake, China.TaxonThe Chinese piebald odorous frog,Odorrana schmackeri.MethodsWe compared body size between insular and mainland populations and between sexes. We examined the potential underlying mechanisms regarding body size shifts using structural equation modelling (SEM). Finally, we analysed changes in diet composition and compared intersexual diet overlap between islands and mainland sites.ResultsWe found insular dwarfism in female but not male frogs. Meanwhile, insular females also had smaller gape widths than mainland females after accounting for snout‐vent lengths (SVLs). According to SEMs, resource availability had a direct positive effect on body size. Finally, diet composition differed between the island and mainland populations but only in females. Males and females on islands exhibited greater overlaps in the diet.Main conclusionsIn contrast with most studies in amphibians, we found insular dwarfism rather than gigantism in females. The smaller gape width after accounting for SVL in insular females suggests potential changes in prey utilization or food availability on these human‐created islands. This notion is further supported by the differentiation of diet composition between island and mainland females. The higher diet overlap between sexes implies stronger intersexual competition for food resources after habitat fragmentation. Overall, we found rapid shifts in morphology and diet in frogs, which might result from habitat fragmentation in only 50 years and underscore the need to consider intersexual differences when assessing responses of species to anthropogenic disturbances.

GENETICS OF INCIPIENT SPECIATION INDROSOPHILA MOJAVENSIS:II. HOST PLANTS AND MATING STATUS INFLUENCE CUTICULAR HYDROCARBON QTL EXPRESSION AND G × E INTERACTIONS

We performed a quantitative trait locus (QTL) analysis of epicuticular hydrocarbon variation in 1650 F(2) males from crosses of Baja California and mainland Mexico populations of Drosophila mojavensis cultured on two major host cacti. Principal component (PC) analysis revealed five PCs that accounted for 82% of the total epicuticular hydrocarbon variation. Courtship trials with mainland females were used to characterize hydrocarbon profiles of mated and unmated F(2) males, and logistic regression analysis showed that cactus substrates, two PCs, and a PC by cactus interaction were associated with mating success. Multiple QTLs were detected for each hydrocarbon PC and seven G x E (cactus) interactions were uncovered for the X, second, and fourth chromosomes. Males from the courtship trials and virgins were used, so "exposure to females" was included as a factor in QTL analyses. "Exposed" males expressed significantly different hydrocarbon profiles than virgins for most QTLs, particularly for the two PCs associated with mating success. Ten QTLs showed G x E (exposure) interactions with most resulting from mainland genotypes expressing altered hydrocarbon amounts when exposed to females compared to Baja genotypes. Many cactus x exposure interaction terms detected across QTL and all PCs confirmed that organ pipe-reared males expressed significantly lower hydrocarbon amounts when exposed to females than when reared on agria cactus. Epicuticular hydrocarbon variation in D. mojavensis is therefore a multigenic trait with some epistasis, multiple QTLs exhibited pleiotropy, correlated groups of hydrocarbons and cactus substrates determined courtship success, and males altered their hydrocarbon profiles in response to females.

GENETICS OF INCIPIENT SPECIATION INDROSOPHILA MOJAVENSIS. I. MALE COURTSHIP SONG, MATING SUCCESS, AND GENOTYPE X ENVIRONMENT INTERACTIONS

Few studies have examined genotype by environment (GxE) effects on premating reproductive isolation and associated behaviors, even though such effects may be common when speciation is driven by adaptation to different environments. In this study, mating success and courtship song differences among diverging populations of Drosophila mojavensis were investigated in a two-environment quantitative trait locus (QTL) analysis. Baja California and mainland Mexico populations of D. mojavensis feed and breed on different host cacti, so these host plants were used to culture F2 males to examine host-specific QTL effects and GxE interactions influencing mating success and courtship songs. Linear selection gradient analysis showed that mainland females mated with males that produced songs with significantly shorter L(long)-IPIs, burst durations, and interburst intervals. Twenty-one microsatellite loci distributed across all five major chromosomes were used to localize effects of mating success, time to copulation, and courtship song components. Male courtship success was influenced by a single detected QTL, the main effect of cactus, and four GxE interactions, whereas time to copulation was influenced by three different QTLs on the fourth chromosome. Multiple-locus restricted maximum likelihood (REML) analysis of courtship song revealed consistent effects linked with the same fourth chromosome markers that influenced time to copulation, a number of GxE interactions, and few possible cases of epistasis. GxE interactions for mate choice and song can maintain genetic variation in populations, but alter outcomes of sexual selection and isolation, so signal evolution and reproductive isolation may be slowed in diverging populations. Understanding the genetics of incipient speciation in D. mojavensis clearly depends on cactus-specific expression of traits associated with courtship behavior and sexual isolation.

Sexual selection and the geography of Plasmodium infection in Savannah sparrows (Passerculus sandwichensis).

According to Hamilton and Zuk's hypothesis of parasite-mediated sexual selection, host-parasite coevolution maintains variation in male genetic quality and allows for strong intersexual selection in species with high rates of infection. In birds, most interspecific tests of this hypothesis relate the prevalence of blood parasites to some measure of the intensity of sexual selection. Such tests often rely on limited sampling of single populations to estimate species-wide infection rates, and many tests are thus vulnerable to intraspecific (geographic) variation in the evolutionary ecology of disease. Here, we used molecular techniques to examine variation in the prevalence of Plasmodium spp. across 14 populations of Savannah sparrows, Passerculus sandwichensis, in eastern North America. Plasmodium could not be detected in any of 68 island birds, but 34 of 119 (29%) mainland males, and 7 of 43 (16%) mainland females were infected. Among mainland birds, infection was common in southern populations but rare in New Brunswick, Canada. Overall, the prevalence of Plasmodium ranged from 0 to 60% across populations, although only 17.8% of birds were infected in the pooled (species-wide) sample. The extent of this geographic variation suggests that limited sampling of single populations is unlikely to yield accurate estimates of species-wide infection rates. However, among mainland Savannah sparrows, the prevalence of malaria correlated strongly with average male size and the degree of sexual size dimorphism. We speculate that either sexual selection leads to male-biased infection or, conversely, that high rates of infection promote the evolution of strong intersexual selection.

Inter‐regime marriage and mobility: The case of mainland China and Taiwan

The recent increasing socioeconomic and political interactions between mainland China and Taiwan have resulted in a significant number of marriages between the two societies. Why do people cross the Strait to look for a marriage partner? What are the socioeconomic and demographic characteristics of such marriages? And what impact do these marriages have on society as well as on the individuals involved? These are the issues we explore in this paper. Analyzing a survey on cross‐Strait marriages conducted by the authors, this paper concludes that inter‐regime marriages between these two societies predominately involve older Taiwanese males and younger mainland females. The general pattern in these marriages represents an exchange between the intrinsic attributes (age, appearance) of the mainland women and the extrinsic attributes (financial status) of the Taiwanese men. In addition, inter‐regime marriages provide a means for mainland women to attain geographic and eventually social mobility.

Decrease in litter size in the shrew Crocidura suaveolens (Mammalia, Insectivora) from Corsica (France): Evolutionary response to insularity?

Populations of the lesser white-toothed shrew, Crocidura suaveolens (Pallas, 1811), from Corsica show an increase in adult body size associated with a decrease in litter size. The average number of embryos in wild Corsican females is smaller (mean 2.6, n = 62) than in mainland females (mean 4.6, n = 173). A breeding experiment was run for 4 years, yielding three generations. Under standard breeding conditions, the differences between island and mainland populations were maintained and were significant (median litter size was 2 for Corsica and 5 for the mainland). These differences in life-history traits were therefore proved experimentally to be genetically determined. Hypotheses concerning the mechanisms responsible for these differences are discussed.

Pre-mating isolation is determined by larval rearing substrates in cactophilicDrosophila mojavensis. II. Effects of larval substrates on time to copulation, mate choice and mating propensity

It has been hypothesized that reproductive character displacement has evolved in mainland Sonora, Mexico populations of cactophilicD. mojavensis due to the presence of a sympatric sibling speciesD. arizonae. In laboratory tests using ancestral Baja California populations and derived, sympatric mainland populations, asymmetrical sexual isolation has been observed among populations ofD. mojavensis where mainland females discriminate against Baja males. Effects of different pre-adult rearing environments on adult mating behaviour were assessed by comparing fermenting cactus tissues like those used in nature for breeding with laboratory media because previous studies have employed synthetic growth media for fly growth and development. Significant behavioural isolation was evident in all cases when larvae were reared on laboratory food, but was non-significant when flies were reared on fermenting cactus, except for the cactus used by most mainland populations, consistent with previous studies. Time to copulation of Baja females was greater than mainland females over all substrates, but male time to copulation did not differ between populations. Time to copulation for both sexes was significantly greater when flies were reared on laboratory food with one exception. The degree of behavioural isolation was weakly correlated with time to copulation across food types (Spearman rank correlation = 0.58,p = 0.099). Therefore, use of laboratory media in this and previous studies exaggerated adult pre-mating isolation and time to copulation in comparison to natural breeding substrates. These experiments suggest that a change in host substrates by saprophagous insects (where chemical differences exist between hosts) may have subtle effects on mating behaviour in a manner which promotes low levels of sexual isolation as a by-product of their utilization of a particular substrate during larval development. ForD. mojavensis, these results suggest that over evolutionary time, radiation into a new environment (from Baja to the mainland) allowed utilization of new host plants that may have incidentally promoted the sexual isolation patterns that have been observed within this species.

Mate choice and pair formation in Timor and Australian Mainland zebra finches

Mate choice and pair formation of captive zebra finches from the Australian mainland, Taeniopygia guttata castanotis, and from Timor, T. g guttata, were compared. In the multiple mate-choice test, an individual could show a preference for perching near a particular bird but could not form a pair bond (e.g. by clumping together). In the pair-formation test, individuals in a flock in an aviary were allowed to form pairs freely. The two subspecies preferred members of their own subspecies in mate-choice tests and mated assortatively in the aviary. When females were presented with Timor males, half of whom had been painted to resemble Mainland males, Timor females both preferred and paired with unpainted Timor males whereas Mainland females approached both unpainted and painted Timor males but paired with the latter. When Mainland males were introduced into the aviary only three out of 10 of these Mainland females re-paired with Mainland males, reflecting the stability of the pair bond. Males and females generally paired with the bird they preferred in the initial mate-choice tests, if that individual was not already paired. In mate-choice tests conducted after pair formation, mott birds preferred the individial they had already paired with. However, those that paired last and had not laid eggs preferred the bird they had chosen in the first mate-choice test rather than the individual they paired with in the aviary.

SELECTION FOR SEXUAL ISOLATION BETWEEN GEOGRAPHIC FORMS OF DROSOPHILA MOJAVENSIS. I. INTERACTIONS BETWEEN THE SELECTED FORMS.

Drosophila mojavensis comprises three geographic forms occurring in the United States, the Baja California peninsula, and mainland Mexico. Peninsular and mainland forms were selected for increased sexual isolation from each other, while controls were maintained with maximum outbreeding. Response to selection was highly asymmetrical in that isolation was very high between selected peninsular males and mainland females, but nonexistent between selected mainland males and peninsular females. The heightened isolation is primarily due to some change in the peninsular males.

Morphological Comparisons of Insular and Mainland Populations of Southeastern White-Tailed Deer

External body measurements were compared among 123 mainland deer from both bottomland swamp and adjoining upland habitats in South Carolina, and 46 deer from a Georgia coastal barrier island. Island deer of both sexes were smaller in length and weight but had longer hair than mainland deer. Female deer from the mainland swamp habitat were smaller in length and weight and had shorter flank hair than females from nearby upland habitats. Male deer from the two mainland habitats showed no differences in either length or weight. Analyses of variance indicated that island deer of both sexes had proportionally smaller body circumferences than their mainland counterparts. Males from the two mainland habitats also differed, with those from the swamp having proportionally larger body circumferences and narrower distances between the eyes. Mainland females also had significantly larger proportional hind foot lengths than did island females. Discriminant function analyses indicated broad overlap among male deer from all three locations, whereas island females were clearly separable from females from the two mainland habitats, which broadly overlapped one another. Body circumference in the case of males and hind foot length in the case of females showed the highest correlations with the discriminant functions for differences between localities. Differences in body length and weight and hair length paralleled similar differences shown earlier for feral swine from the same island and mainland habitats. These similarities suggest that the differences observed are probably not the result of random genetic drift or founder effect.

Are There Genetic Revolutions in Island Populations of Drosophila algonquin?

A study of island and mainland populations of Drosophila algonquin in Maine was undertaken in order to detect any genetic incompatibility between them. Inbreeding has significant deleterious effects on the egg to adult survival of these flies, but not on their developmental rate. Although island populations probably are descended from a small number of founders and are much smaller than those on the mainland, they manifest no deleterious consequences of inbreeding. In fact, offspring produced by island derived females have significantly faster development than those produced by mainland females. Island and mainland derived flies show no evidence of genetic incompatibility, as the number, developmental time, and sex ratio of progeny produced by island x mainland crosses were not significantly different from those produced by intra-population crosses. Hence, island populations of D. algonquin show no evidence of having undergone genetic revolutions.

Comparison of Lipid Cycles of Holbrookia propinqua from Padre Island and Mainland Texas

We previously showed that mean clutch size of Holbrookia propinqua from the Texas mainland was significantly larger than that of lizards from Padre Island (* = 4.7 mainland, * = 3.2 island) and we provided indirect evidence that mainland females lay an average of four clutches each year while island females produce three clutches. Despite their greater egg production, main- land females are smaller than island females. Thus, we studied H. propinqua from Padre Island and mainland Texas to assess the correlation of their differing reproductive potentials and body size with patterns of lipid deposition and utilization. The patterns of lipid deposition and utilization were similar in island and mainland populations. There was a significant positive correlation between lipid weight and SVL in juveniles. Juveniles used stored lipid for winter maintenance and/or growth in early spring. The quantity of lipid stored was generally similar in island and mainland counterparts, but adult females had signifi- cantly more fat than adult males of the same population due to the presence of yolk lipids. We suggest that the major difference in the two populations is not in the quantity of lipid stored prior to reproduction, but in the proportion of the total energy budget that is devoted to reproduction. Mainland lizards are probably smaller in size than island lizards because food availability is less and because a larger share of ingested energy is devoted to reproduction and associated activities rather than to somatic growth.

A Breeding Season Difference in Two Populations of the Australian Macropod Marsupial (Setonix brachyurus)

The population of Setonix at Rottnest Island (Western Australia) has a season of birth restricted to 6 months, but the population on the adjacent mainland was found during this study to breed continuously throughout the year. As both populations are in the same latitude and less than 50 miles apart, it is unlikely that climatic conditions are responsible for the different breeding patterns. Previous work showed that the Rottnest Island population annually suffered semistarvation in the late summer. This recurrent population debility is thought to be the main factor maintaining the 6-month anestrous period, as females from Rottnest Island maintained in captivity on liberal rations are known to decrease, and after a period of 2 or more years, finally delete the anestrous period. The period of gestation and pouch life of Setonix is a little longer than 6 months. Mainland females, breeding continuously, will produce 2 joeys in a little over a year, but Rottnest Island females which have only 1 young each year are also forced to delay their first joey 6 months. The decreased fertility of the insular population as a result of the 6-month anestrous period and later breeding may then be regarded as a population-limiting factor, only affected by long-term environmental changes but acting in concert with the short-term Malthusian factors of disease and starvation. A possible adult age structure difference resulting from the anestrous period is also discussed.