A study of nonrandom mating in a British population of the two-spot ladybird with a high frequency of the melanic morph

In some studies of the two-spot ladybird (Adalia bipunctata), melanic males have been found in excess over the typical morph in matings. Data suggest that a genetic female mating preference is responsible. The mating advantage of melanic males may be important in maintaining a polymorphism between melanic and typical ladybirds in many populations in the United Kingdom (U.K.). It has been reported that preference frequency varies linearly with melanic frequency throughout most of the U.K. One particular population ofAdalia bipunctata near Aberdare, South Wales, is noted for its high frequency of melanic individuals. It has been suggested that local environmental factors account for the high melanic frequency in this population. It is also possible, however, that a female mating preference may be at least partly responsible for the high frequency of melanics (as has been proposed for the rest of the U.K.). In this study, experiments have been performed to determine the level of female mating preference in the Aberdare population. No evidence was found for any mating advantage to melanic males. There was inconsistent and unexpected evidence that melanic females were overrepresented in matings, but the cause for this was unclear. Female mating preference does not appear, therefore, to be responsible for the high melanic frequency in the population ofAdalia bipunctata near Aberdare. There is not a simple association between mating preference and melanic frequency in U. K. populations of the two-spot ladybird.     

Ventral pigmentation variation in the meadow spittlebug Philaenus spumarius (L.) (Hemiptera,Cicadomorpha: Cercopidae)

The meadow spittlebug Philaenus spumarius (L.) (Hemiptera, Cicadomorpha: Cercopidae) exhibits heritable colour/pattern variation on the dorsal and ventral sides of the adults. Eleven principal dorsal morphs are grouped as melanics and non-melanics according to the pigmentation of the dorsal surface. An investigation of ventral pigmentation variation in Philaenus spumarius was carried out with laboratory breeding stock obtained from Llysdinam, Wales. Analyses of the 1552 individuals, 753 females and 799 males, indicated that the pigmentation on the ventral surface of the adult individuals which vary significantly is associated with dorsal morph. Ventral parts of the dorsal melanics are usually darker than in non-melanics in both females (Kruskal-Wallis one-way ANOVA: H = 372.70, d.f. = 7, P < 0.001) and males (H = 407.36, d.f. = 7, P < 0.001). The combined “C” group morphs (flavicollis + gibbus + leuco- cephalus) are always darker than all other morphs in both sexes.     

Fungi Vectored by the Bark Beetle Ips typographus Following Hibernation Under the Bark of Standing Trees and in the Forest Litter

The bark beetle Ips typographus has different hibernation environments, under the bark of standing trees or in the forest litter, which is likely to affect the beetle-associated fungal flora. We isolated fungi from beetles, standing I. typographus-attacked trees, and forest litter below the attacked trees. Fungal identification was done using cultural and molecular methods. The results of the two methods in detecting fungal species were compared. Fungal communities associated with I. typographus differed considerably depending on the hibernation environment. In addition to seven taxa of known ophiostomoid I. typographus-associated fungi, we detected 18 ascomycetes and anamorphic fungi, five wood-decaying basidomycetes, 11 yeasts, and four zygomycetes. Of those, 14 fungal taxa were detected exclusively from beetles that hibernated under bark, and six taxa were detected exclusively from beetles hibernating in forest litter. The spruce pathogen, Ceratocystis polonica, was detected occasionally in bark, while another spruce pathogen, Grosmannia europhioides, was detected more often from beetles hibernating under the bark as compared to litter. The identification method had a significant impact on which taxa were detected. Rapidly growing fungal taxa, e.g. Penicillium, Trichoderma, and Ophiostoma, dominated pure culture isolations; while yeasts dominated the communities detected using molecular methods. The study also demonstrated low frequencies of tree pathogenic fungi carried by I. typographus during its outbreaks and that the beetle does not require them to successfully attack and kill trees.     

Industrial melanism in the moths, Diurnea fagella (Oecophoridae) and Allophyes oxyacanthae (Caradrinidae)

Comparative studies of melanism in the two cryptic moth species, Diurnea fagella (Denis & Schiffermüller) and Allophyes oxyacanthae (L.), have been carried out in southern England and south Wales. Estimates of the relative crypsis of the melanic and typical forms of both these species have been made at a number of sites and these were compared with the melanic frequencies in samples from these sites. These comparisons showed that selective prédation could be a major factor in the variation of melanic frequencies of both of these species. A consideration of the spread of melanism in these species suggests that non-visual selection may favour the melanics of D. fagella in urban areas and that non-visual selection, not closely associated with urban conditions, may be responsible for the restriction of melanics in A. oxyacanthae to Britain. The results for these two species are discussed in relation to investigations of melanism in other moth species.     

Genetic control of colour /pattern polymorphism in British populations of the spittlebug Philaenus sputnarius (L.) (Homoptera: Aphrophoridae)

The results of breeding experiments designed to determine the genetic control of the colour/pattern polymorphism in Philaenus spumarius in certain British populations are described and contrasted to previously published results for material taken from populations in southern Finland. The 11 principal phenotypes are controlled by seven alleles at a single autosomal locus, with complex patterns of dominance and co-dominance. In Finland, and most of the rest of the species' extensive range, the eight melanic morphs are wholly or substantially limited to the females, in which they are dominant to the typical form. Previously, this sex limitation has been explained in terms of reduced penetrance of melanic alleles in males and/or dominance reversal between the sexes, such that the eight melanic phenotypes (controlled by five alleles which are adjacent in the dominance heirarchy) are dominant to typical in the females but recessive in the males. Published data on morph frequencies in S Finland and on breeding experiments using material collected from these populations are re-examined and it is shown that neither theory accounts adequately for all the evidence. By contrast, in most British populations there is greatly increased penetrance in males of the melanic morphs which are strictly female-limited elsewhere. Breeding experiments, using P. spumarius taken from selected British populations, provide clear evidence that melanics are dominant to typical in both sexes. This difference in genetic control is entirely consistent with the balance of morph frequencies between the sexes in the populations from which the breeding material for the two separate studies was taken. Experimental material for this study was taken from populations in the Cynon Valley in south Wales, which have the highest melanic frequencies in the species' range and show particularly clear expression of melanic phenotypes in males. Both of these features are strongly correlated with severe aerial pollution from a local smokeless fuel factory. Selection for melanism in these populations is clearly strong, which probably accounts for the high level of penetrance and the dominance of melanics to typical in both sexes. Although further experiments are needed, it is suggested that regulatory loci, controlling the penetrance and expression of melanic alleles in males, could account for the observed differences in genetic control between populations in Britain and Finland.     

Seasonal cycles of assortative mating and reproductive behaviour in polymorphic populations of Harmonia axyridis in China

Abstract 1. We observed native populations of Harmonia axyridis (Pallas) around Beijing, China, over 2 years and performed choice and no‐choice mating tests between melanic and succinic (non‐melanic) beetles in the laboratory. 2. Succinic phenotypes outnumbered melanics by 5:1 in autumn, but melanics became equally abundant in spring, supporting previous inferences that melanism is advantageous in winter, but costly in summer. 3. Female H. axyridis expressed mate preference overtly, by rejecting less‐preferred phenotypes, and cryptically, by retaining their eggs for longer periods after matings with less‐preferred males, ostensibly to replace their sperm. 4. Succinic pairs formed more quickly in the spring generation, and melanic pairs in the autumn, and the time to copula was affected by both male and female phenotype. The strength of mate preference was contingent on female phenotype, suggesting melanic alleles had pleiotropic effects. 5. Whereas pair formation was under female control, the duration of copula was under male control and lasted longer in the autumn generation than in the spring. Copulations in the choice test tended to be shorter between similar phenotypes, suggesting that males invested more in dissimilar females when alternative mates were available. 6. Although spring and autumn generations were raised under identical conditions, significant contrasts were observed in their reproductive behaviour. 7. Two alternative hypotheses are advanced to explain why gender‐specific reproductive behaviours might vary between generations: maternally‐mediated epigenetic factors that influence the expression of genes in progeny as a function of maternal environment, and linkage disequilibria among alleles that cycle in frequency seasonally as a function of assortative mating.     

Thermal biology of the common garter snake Thamnophis sirtalis (L.)

Summary The thermoregulatory significance of a striped-melanic colour polymorphism in the common garter snake, Thamnophis sirtalis, was assessed through a combination of labortory experimentation and field study. In experiments with living snakes the melanic morph maintained a higher body temperature than the striped morph, when exposed to natural insolation. Experiments with excised skin showed that this thermal advantage is attributable to some integumental difference between the two morphs. Body temperatures of snakes in the field revealed that, during the colder part of the active season, melanics were able to stay warmer than striped snakes by an amount (1.24 C°) approximating the difference observed in the laboratory. Some evidence and argument is presented to suggest that melanism also may confer protection against overheating in warm periods.     

Industrial and non-industrial melanism in the peppered moth, Bistort betularia (L.)

Abstract. 1. Estimates of the relative crypsis of the melanic and typical morphs of B.betularia have been made at fifty-two sites in southern England and south Wales and these estimates were compared with melanic frequencies in samples from these sites.
2. The decrease from east to west in the frequency of the melanic form, carbonaria , and increase in the frequency of a second melanic form, insularia , across the southern part of England and Wales is largely independent of changes in smoke concentration, sulphur dioxide concentration or relative crypsis.
3. When all the available information on the distribution of the melanics of B.betularia is considered, sulphur dioxide concentration is correlated with the geographic variation in carbonaria frequency. This, together with evidence of the close relationship between carbonaria crypsis and sulphur dioxide levels, indicates that outside southern England and south Wales, either selective predation, or some direct selective effect of pollutants, is of major importance in determining the variation in carbonaria frequency.
4. Some features of the pattern of the spread of carbonaria in England and Wales during the last century give reasons for expecting non-industrial selective factors to be of greater importance in determining the distribution of melanics of B.betularia in southern England and south Wales than in the rest of Britain.     

A steep cline in ladybird melanism has decayed over 25 years: a genetic response to climate change?

A cline in the frequency of melanic morphs of the two-spot ladybird, Adalia bipunctata, was first surveyed in 1980 along a transect extending inland from the coast in the Netherlands. At that time, the frequency of melanics increased over some 40 km from 10% near the coast to nearly 60% inland. Additional surveys made in 1991 and 1995 demonstrated some progressive change in cline shape. New samples from 1998 and 2004 confirm these dynamics, and show that over a period of about 50 generations for the beetle, the cline had decayed rapidly to yield rather uniform frequencies of melanic morphs at around 20% along the whole transect by 2004. Climate data and evidence for thermal melanism in this species support our contention that these dynamics reflect a dramatic example of a rapid genetic response within populations to climate change and local selection.     

Maturation of post-hibernation flight behaviour in the Coccinellid Coleomegilla maculata (DeGeer)

Summary Coleomegilla maculata flies from its hibernation sites to breeding areas in the spring. Flight behaviour among the hibernating beetles was studied using the tethered flight technique. It was found that there is a successive maturation of flight behaviour in the spring. This process is mainly controlled by temperature acting over an extended period. From a standstill at 15°C the rate of the maturation process increased as the temperature was raised. Short photoperiods exerted a depressing effect on glight development early in the winter, but later this effect disappears.     

Predation of ladybird beetles by the orb-web spider <Emphasis Type="Italic">Araneus diadematus</Emphasis>

Ladybirds face a diversity of potential predators from which their main protection is powerful alkaloid-based chemical defence. In the laboratory, adults of the European orb-web spider Araneus diadematus Clerck readily consumed the native European ladybird Coccinella septempunctata L. and non-melanics and melanics of the exotic Harmonia axyridis (Pallas). The spider was little deterred by their defensive chemistry and apparently suffered no ill effects after eating ladybirds. This is particularly notable for H. axyridis, which possesses a novel alkaloid not known from European ladybirds and to which European predators are not expected to be adapted. Examination of inhabited A. diadematus webs and experimental determination of for how long captured ladybirds remained in webs indicated that ≤2% of spiders consume a ladybird each day. Ladybirds and A. diadematus are probably complementary rather than antagonistic in controlling crop pests, with ladybirds being at greatest risk from A. diadematus predation in autumn, during migration to overwintering sites.     

Selective bird predation on the peppered moth: the last experiment of Michael Majerus

Colour variation in the peppered moth Biston betularia was long accepted to be under strong natural selection. Melanics were believed to be fitter than pale morphs because of lower predation at daytime resting sites on dark, sooty bark. Melanics became common during the industrial revolution, but since 1970 there has been a rapid reversal, assumed to have been caused by predators selecting against melanics resting on today's less sooty bark. Recently, these classical explanations of melanism were attacked, and there has been general scepticism about birds as selective agents. Experiments and observations were accordingly carried out by Michael Majerus to address perceived weaknesses of earlier work. Unfortunately, he did not live to publish the results, which are analysed and presented here by the authors. Majerus released 4864 moths in his six-year experiment, the largest ever attempted for any similar study. There was strong differential bird predation against melanic peppered moths. Daily selection against melanics (s ≈ 0.1) was sufficient in magnitude and direction to explain the recent rapid decline of melanism in post-industrial Britain. These data provide the most direct evidence yet to implicate camouflage and bird predation as the overriding explanation for the rise and fall of melanism in moths.     

Predation and the persistence of melanic male mosquitofish (Gambusia holbrooki)

The empirical reasons for the persistent rarity of a genotype are typically complex and tedious to identify, particularly in nature. Yet rare morphs occur in a substantial fraction of phenotypic polymorphisms. A colour polymorphism has persisted for decades in the eastern mosquitofish, yet why this is so remains obscure. Here, I report the results of (1) intensive sampling at 45 natural sites to obtain the frequency distribution of the melanic (black) mosquitofish morph in Florida, (2) predation trials, conducted independently in mesocosms, with three different predatory species and (3) two mark-recapture studies, conducted in nature. This work (1) documents the rarity of melanic mosquitofish in nature, (2) demonstrates that melanic males experience a selective advantage over silver males in the presence of predators, (3) indicates no difference in the colour morphs' survival at a natural site essentially devoid of these predators, although suggesting a higher rate of recapture for melanic males at a site rife with predators. Overall, selective predation appears to contribute to the persistence of the melanic morph, despite its rarity in nature.     

Further experiments on resting site selection by the typical and melanic forms of the moth, Allophyes oxyacanthae (Caradrinidae)

The melanic and typical morphs from 13 families of the moth, Allophyes oxyacanthae (Linnaeus) were tested for evidence of resting site selection in a large box lined with oak bark of three reflectances. For 12 of the families, one or both of the parents originated from two families, 0/1 and 0/3, which had been tested in a similar manner in the previous year. In all of these 12 families typicals showed a preference for the palest background available, "light grey". The melanic results for the same families were significantly heterogeneous but could be partitioned on the basis of parentage, into six families in which melanics preferred light grey, and six families in which melanics preferred the background on which they are most cryptic, dark grey. In the only family in which neither of the parents originated from either 0/1 or 0/3, both typical and melanics showed a preference for the background on which typicals are most cryptic, bare bark. The results of the two years' experiments indicate that it is necessary to postulate that, in addition to the pleiotropic effects of alleles at the melanic locus, another locus (or loci) is involved in the control of resting site selection.     

Changes in renal morphology and renin secretion in the golden-mantled ground squirrel (Spermophilus lateralis) during activity and hibernation

Summary Chronological changes in renal glomerular morphology and plasma renin activity were investigated during active and hibernating periods in the golden-mantled ground squirrel Spermophilus lateralis. The objective of this study was to determine whether the glomerular endothelium, visceral epithelium (podocytes), basement membrane, mesangial cells, proximal convoluted tubule cells and plasma renin activity exhibit measurable sequential differences between as well as within active and hibernating states at various time points. Limitations in the size of the experimental population prevented an evaluation of changes in these parameters during other important periods such as periodic arousal between hibernation bouts. In this study, glomerular endothelial pore number and epithelial filtration slit number significantly decreased by early hibernation when compared to those during summer activity, and then they increased back toward summer levels by late hibernation. In contrast, podocytic pedicel width along the glomerular basement membrane increased from summer activity to early hibernation, before significantly decreasing again by late hibernation. Mesangial cell and proximal convoluted tubule cell activity appeared increased during hibernation as compared to summer activity, whereas the width of the glomerular basement membrane showed no significant alterations throughout. Plasma renin activity significantly increased during early hibernation and mid-hibernation when compared to summer levels but had decreased by late hibernation toward summer values. The glomerular and plasma renin activity changes observed in this study clearly illustrate the drastic structural and functional adjustments which hibernating species make during torpor and also correlate well with the reported decrease in renal perfusion pressure and urine formation during hibernation. The observed morphological changes during hibernation do not appear to be temperature-dependent, because significant alterations in most of the parameters studied occurred during this period despite the fact that cold-room temperatures were kept constant throughout. The chronological approach to this study and its morphometric evaluation represent a pilot attempt at accurately documenting these changes during two critical states in the hibernator's cycle and may eventually lead to the characterization of these changes during the entire circannual cycle.     

Industrial melanism and peppered moths (Biston betularia (L.))

The spread of melanic forms of the peppered moth ( Biston betularia (L.)) over polluted areas of Britain from the mid-nineteenth century onwards, has become widely known and quoted as a classical example of microevolutionary change. Probably the most important factor in the spread (and subsequent decline, following the Clean Air Act) of the melanics has been bird predation on less cryptic individuals, but a range of other factors may also affect the maintenance of allele frequencies at any one place (site selection, dispersion, heterosis, frequency dependent selection, larval hardiness, etc). The development of the "Peppered Moth Story" is described, and suggestions made about needed research.     

Fitness consequences of pheromone production and host selection strategies in a tree-killing bark beetle (Coleoptera: Curculionidae: Scolytinae)

Timing of arrival at a resource often determines an individual’s reproductive success. Tree-killing bark beetles can reproduce in healthy trees by attacking in adequate numbers to overcome host defences that could otherwise be lethal. This process is mediated by aggregation and antiaggregation pheromones. Beetles that arrive early in such a “mass attack” must contend with undiminished tree defences, and produce enough pheromones to attract more beetles, but have a head start on gallery construction and egg-laying. Beetles that arrive late may be impeded by competition and diminishing availability of phloem, but should experience fewer costs associated with pheromone production and battling tree defences. We investigated relationships between timing of arrival, body size, pheromone production and fitness in the southern pine beetle, Dendroctonus frontalis. In field experiments, we captured beetles that arrived early (pioneers) and late on slash pine trees, Pinus elliottii, and measured pheromone amounts in their hindguts. We marked gallery entrances of beetles as they landed on a tree and measured their reproductive success after the attack terminated. We found no difference in body size or pheromone amounts between early and late arrivers. Most beetles arrived at the middle of the attack sequence, and excavated longer galleries per day than early arrivers. The number of offspring produced per day by beetles that established galleries midway through mass attack was higher than those that arrived early or very late in the sequence. Our results suggest that beetles do not exhibit adaptive phenotypic plasticity in pre-landing pheromone production, depending on the extent of previous colonisation of a host. Rather, it appears that stabilising selection favours beetles that attack in the middle of the sequence, and contributes to attack synchrony. Synchronous attack on trees is essential before population booms characteristic of tree-killing bark beetles can occur in nature.     

A countrywide survey of colour morph frequencies in the spider Enoplognatha ovata (Glerck) (Araneae: Theridiidae): evidence for natural selection

Data on the frequencies of the main colour morphs ( lineata, redimita and ovata ) of Enoplognatha ovata have been collected from a total of 454 Ordnance Survey 10 km squares distributed throughout Great Britain. Only c. 0.5% of samples were monomorphic, for lineata in each case. Multiple regression analysis has been used to assess possible associations between morph frequencies and principal components derived from nine environmental variables. The distribution of morph frequencies is not random but shows weak clines associated with certain climatic factors. These large scale clines indicate the action of natural selection although very local variations in morph frequencies may result from selection and/or drift.     

Survival rates in a small hibernator,the edible dormouse: a comparison across Europe

Understanding how local environmental factors lead to temporal variability of vital rates and to plasticity of life history tactics is one of the central questions in population ecology. We used long‐term capture‐recapture data from five populations of a small hibernating rodent, the edible dormouse Glis glis, collected over a large geographical range across Europe, to determine and analyze both seasonal patterns of local survival and their relation to reproductive activity. In all populations studied, survival was lowest in early summer, higher in late summer and highest during hibernation in winter. In reproductive years survival was always lower than in non‐reproductive years, and females had higher survival rates than males. Very high survival rates during winter indicate that edible dormice rarely die from starvation due to insufficient energy reserves during the hibernation period. Increased mortality in early summer was most likely caused by high predation risk and unmet energy demands. Those effects have probably an even stronger impact in reproductive years, in which dormice were more active. Although these patterns could be found in all areas, there were also considerable differences in average survival rates, with resulting differences in mean lifetime reproductive success between populations. Our results suggest that edible dormice have adapted their life history strategies to maximize lifetime reproductive success depending on the area specific frequency of seeding events of trees producing energy‐rich seeds.