Polymorphic Müllerian mimicry and interactions with thermal melanism in ladybirds and a soldier beetle: a hypothesis

It is argued that groups of similarly coloured species of coccinellids are Müllerian mimicry rings. This is based on a synthesis of the literature about the nature of their biology and aposematic colour patterns, their highly developed chemical defence and the responses of bird predators to them. The system of multiple mimicry ‘rings’ is illustrated for the Dutch coccinellid fauna. Some polymorphic species, including Adalia, exhibit red forms and black melanic forms which are apparently components of different putative mimicry rings. A similar reasoning is put forward with regard to the orange and the black forms of the soldier beetle Cuntharis livida. Hypotheses involving spatial variation in comimics, as have been developed to account for some other cases of polymorphic Miillerian mimicry, predict that sympatric polymorphic species exhibiting similar sets of phenotypes will show parallels in their geographical variation. This is tested for A. bipunctata and A. decempunctata in The Netherlands. On this local scale there is no parallel variation; A. bipunctata exhibits marked geographical differentiation whereas A. decempunctata shows a general uniformity in morph frequency. Observations on their population biology show that only in A. bipunctata is there a major spring period of adult reproduction on shrubs exposed to direct sunshine. Previous work has demonstrated an influence of thermal melanism in this period of the life cycle. It is suggested that local responses in species such as A. bipunctata may reflect a partial ‘escape’ from stabilizing aposematic selection. The basis of a steep cline found in C. livida, which opposes one in A. bipunctata, is unknown and unlikely to be related to mimicry. There is some evidence that the polymorphism is influenced by non-random mating. When species and communities of coccinellids are considered on a wide geographical scale many observations about their colour patterns and spatial variation, especially those of Dobzhansky, support an interaction between selection favouring mimetic resemblance and forms of climatic selection, especially thermal melanism. The polymorphism in Adalia is discussed in relation to a system of multiple mimicry rings and to Thompson's recent theoretical treatment of the maintenance of some polymorphisms for warning coloration by a balance between aposematic and apostatic selection. This becomes more tenable in coccinellids because of evidence that bird predators show a variable response to them. Frequency-independent selection arising from thermal melanism can provide the basis of spatial variation in equilibrium points. An alternative to such a hypothesis is one in which differences in unpalatability between species of coccinellids are emphasized (after experiments of Pasteels and colleagues). Some less unpalatable species such as Adalia may have responded to periods of prolonged disruptive selection acting in a frequency-dependent way to promote polymorphic mimicry associated with different modal colour patterns and intermediate in nature between classical Batesian and Müllerian mimicry. The likely occurrence of a supergene controlling polymorphism in some coccinellids is consistent with such an explanation.     

Phenotypic variation in colour pattern and seasonal plasticity in Eristalis hoverflies (Diptera: Syrphidae)

Abstract.

• 1 An examination of phenotypic variation in colour pattern was carried out on four Eristalis hoverfly species using museum material.
• 2 The amount of phenotypic variation varied substantially among the species with E.arbustorum being the most variable. The other species showed a wide colour pattern range but less variation within that range (E.abusivus and E.nemorum), or a narrow range of colour variation (E.horticola).
• 3 Sexual colour dimorphism was apparent in all four species, but most pronounced in E.abusivus and E.nemorum.
• 4 There were good phenotype-season relationships shown by both sexes in all species, except for female E.abusivus and E.nemorum, with paler insects being more abundant during the warmer summer months.
• 5 Female, but not male, E.arbustorum collected at inland sites were on average paler than those collected at coastal sites. This observation is considered with respect to temperature during the developmental stages.
• 6 The function of colour plasticity in hoverflies is discussed with reference to the need to maintain optimal thermal conditions for activity.

     

A stable,genetically determined colour dimorphism in the dung beetle Aphodius depressus: patterns and mechanisms

1. Melanism – the occurrence of dark morphs – in insects has been attributed to differences in, among other things, thermoregulation and immune defence. Dark individuals are hypothesised to perform better in colder areas, and to exhibit stronger melanin‐based immune defence. 2. In the present study, the geographical distribution of two colour morphs in Aphodius depressus (Kugelann), its climatic correlates, and temporal stability was described. Underlying mechanisms were then targeted through experiments: the inheritance of colour through controlled crosses, heating rates by thermal imaging, physiological tolerance by critical thermal limits, and immune efficiency by melanisation of implants. 3. In A. depressus, colour appears inherited by simple Mendelian principles, with red dominating over black. The frequency of two colour morphs forms a large‐scale cline. In the South West of Finland, all individuals are black, whereas, in the North East, most are red. This pattern has remained constant over 13 years (1996–2008). 4. The geographical pattern was not attributable to thermoregulation: black morphs were more abundant in warmer rather than colder parts of the country. In experiments, we found no differences in the heating rate of the two morphs, or in their upper temperature maxima. Neither did the morphs differ in their response to artificial objects inserted in their haemolymph. 5. Overall, colour variation in A. depressus occurs as a stable, genetically determined dimorphism, governed by Mendelian inheritance. Yet, no support for prevailing theory of factors sustaining melanism was found. The reasons for colour polymorphism in insects may thus be complex, and should be sought on a case‐by‐case basis.     

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.     

Do current hypotheses explain continental and seasonal variation in female morph frequencies of the damselfly,Nehalennia irene?

Female-limited colour polymorphism occurs in many damselfly species, where one morph resembles the male (andromorph) and the other is dissimilar (gynomorph). Explanations for this phenomenon vary, but most assume that andromorphism has arisen in odonates, as a response to excessive male harassment. Here, we quantify the extent of continental and seasonal variation in female morph frequencies in a widely-distributed damselfly and ask whether the spatiotemporal patterns in andromorph frequency can be understood on the basis of sexual harassment theory. We sampled the damselfly, Nehalennia irene (Hagen) among regions across Canada, and at several sites, over the reproductive season, within Central Canada. Andromorph frequencies ranged from 0 to > 90% across Canada. In particular, sites in Western Canada had consistently high andromorph frequencies, whereas andromorph frequencies among Central sites were lower and variable and, among Eastern sites, were lower still (except one site) and relatively invariant. For populations in Central Canada, both andromorph frequencies and population densities varied significantly over time, reaching a peak mid-season. As expected, morph frequency covaried significantly with estimates of male harassment in some cases, but estimates of male harassment did not consistently account for variation in morph frequencies within all regions. Additional factors such as genetic drift may influence morph frequency at the edge of a species' range. Future work also should test, and attempt to explain causation, for seasonal variation in morph frequency.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 501–508.     

An experimental study of ontogenetic and seasonal changes in the temperature preferences of unfed and fed brown trout,Salmo trutta

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Effects of phenotypic variation onto body temperature and flight activity in a polymorphic insect

Abstract.  According to biophysical principles, colour and size are important phenotypic factors that may influence body temperature and activity in ectothermic insects. In taxa showing female-limited polymorphism, males and female morphs differ in body colour, size and activity pattern. However, no previous study has evaluated whether such phenotypic and behavioural variation relates to differences between males and female morphs in thermal properties. In the present study, the relationships between body colour, size, activity and body temperature are examined under laboratory and field conditions, for the polymorphic damselfly Enallagma cyathigerum (Charpentier, 1840) (Odonata: Zygoptera). Contrary to expectation, males and female colour morphs of this species do not differ in thermal properties (i.e. heating characteristics or field body temperatures). When questioning phenotype and activity, temperature does not appear to be relevant for understanding the maintenance of female-limited polymorphism.     

Geographic variation of color polymorphism in two sibling ladybird species,Harmonia yedoensis and H. axyridis (Coleoptera: Coccinellidae)

Geographical variation of elytra color pattern in two sibling ladybird species, Harmonia yedoensis and H. axyridis (Coleoptera: Coccinellidae), was examined. The two species are distributed sympatrically in central Japan; however, only H. yedoensis and H. axyridis occur in the Ryukyu Islands (southern Japan) and Hokkaido island (northern Japan), respectively. The frequency of elytra color patterns was significantly different between the two species in all sympatric locations and our results were inconsistent with the classical theory on Müllerian mimicry. The most dominant pattern of H. axyridis was the least dominant of H. yedoensis in all sympatric populations. Furthermore, the frequency of the non‐melanic form (red ground color with or without black spots) increased towards the south in H. yedoensis. This tendency was in contrast to the known geographical cline in H. axyridis in which the melanic form (black ground color with red spots) was gradually displaced with the non‐melanic form northwards in the Japanese archipelago. We discuss possible selective factors including predator avoidance, thermal adaptation and reproductive character displacement, all of which might contribute to the maintenance of the color polymorphism in the two Harmonia species.     

Tenebrionid beetles in the shortgrass prairie: daily and seasonal patterns of activity and temperature

ABSTRACT. 1. Patterns of daily and seasonal activity for seven species of tenebrionid beetles, genus Eleodes , were investigated in the shortgrass prairie of northeastern Colorado. The relationship between time of activity, body temperatures, and rates of water loss of the beetles was examined in the field and in laboratory experiments.
2. Common species were active from April until the end of October; however, asynchronous peaks of abundance occurred.
3. Beetles were diurnally active with peaks of daily activity occurring 2–4 h after sunrise and before sunset. Less than a 2 h shift in mean time of activity occurred between seasons.
4. Within species, body temperatures measured in the field closely corresponded to temperatures selected in an experimental thermal gradient; hence, species seemed to prefer particular body temperatures and were most active during times when those temperatures could be achieved. Body temperatures measured in the field approximated ambient temperatures measured in the vicinity of the beetle.
5. Significant differences among several species were found for times of daily activity and corresponding body temperatures.
6. Ability to resist water loss by evaporation was not correlated with daily or seasonal activity patterns.     

Natural selection and the distribution of shell colour morphs in three species of Littoraria (Gastropoda: Littorinidae) in Moreton Bay, Queensland

The distribution of yellow, brown and red morphs of sympatric species of Littoraria were recorded on mangrove trees of the genus Avicennia within Moreton Bay, Queensland. The roles of background mimicry (leaf vs. bark, dark vs. light), niche selection and thermal tolerance (sunny vs. shaded positions and height above ground) were examined. The yellow advantage found previously in the area was tested. Total yellow morph frequency adjusted to a reduction in leaf background on pruned trees. Morph frequencies in Littoraria species reflect differences in habitat use. L. filosa (high yellow frequency) was more frequently found on leaves at the highest tree levels, while L. luteola (high brown frequency) was more frequently found on branches at lower levels. It is therefore argued that morphs mimic background elements. Previously reported niche selection by yellow and brown morphs of leaf and bark backgrounds is shown to be a result of the distribution of L. luteola on branches and L. filosa on leaves. At warmer times of the year, yellow L. filosa were more common in sunny positions; this is thought to be a result of thermal tolerance. There appears to be some advantage to particular morphs on particular tree types, but this relationship needs to be examined further. Mangrove-dwelling Littoraria are a promising model to investigate molluscan polymorphism. In the past, erroneous identification of sympatric species may have influenced the accuracy of reported patterns. We used allozyme electrophoretic markers as a precise identification technique. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 219–232.     

Critical thermal limits in Mediterranean ant species: trade-off between mortality risk and foraging performance

1. In Mediterranean ant communities, a close relationship has been found between activity rhythm in the period of maximum activity and position in the dominance hierarchy: subordinate species are active during the day, when conditions are more severe, while dominants are active during the afternoon and the night.
2. Results obtained in this study confirmed that the species foraging at higher temperatures were closer to their critical thermal limits than the species foraging at lower temperatures.
3. This enabled two extreme strategies of foraging in relation to temperature to be distinguished: (1) heat-intolerant ant species behaved as risk-averse species, foraging at temperatures very far from their critical thermal limits; and (2) heat-tolerant ant species behaved as risk-prone species, foraging very near their critical thermal limits and running a high heat mortality risk.
4. Heat-tolerant species benefited from this strategy by having better foraging performance at high temperatures.
5. This wide range of thermal niches may be one reason why Mediterranean ant faunas are so diverse in the face of limited diversity in vegetation and habitat structure: the daily range of temperature may be sufficiently great to meet the requirement both of heat-adapted and cold-adapted species as well as a spectrum of intermediate forms.     

Acclimation of snow gum (Eucalyptus pauciflora) leaf respiration to seasonal and diurnal variations in temperature: the importance of changes in the capacity and temperature sensitivity of respiration

We investigated the relationship between daily and seasonal temperature variation and dark respiratory CO₂ release by leaves of snow gum (Eucalyptus pauciflora Sieb. ex Spreng) that were grown in their natural habitat or under controlled‐environment conditions. The open grassland field site in SE Australia was characterized by large seasonal and diurnal changes in air temperature. On each measurement day, leaf respiration rates in darkness were measured in situ at 2–3 h intervals over a 24 h period, with measurements being conducted at the ambient leaf temperature. The rate of respiration at a set measuring temperature (i.e. apparent ‘respiratory capacity’) was greater in seedlings grown under low average daily temperatures (i.e. acclimation occurred), both in the field and under controlled‐environment conditions. The sensitivity of leaf respiration to diurnal changes in temperature (i.e. the Q₁₀ of leaf respiration) exhibited little seasonal variation over much of the year. However, Q₁₀ values were significantly greater on cold winter days (i.e. when daily average and minimum air temperatures were below 6° and –1 °C, respectively). These differences in Q₁₀ values were not due to bias arizing from the contrasting daily temperature amplitudes in winter and summer, as the Q₁₀ of leaf respiration was constant over a wide temperature range in short‐term experiments. Due to the higher Q₁₀ values in winter, there was less difference between winter and summer leaf respiration rates measured at 5 °C than at 25 °C. The net result of these changes was that there was relatively little difference in total daily leaf respiratory CO₂ release per unit leaf dry mass in winter and summer. Under controlled‐environment conditions, acclimation of respiration to growth temperature occurred in as little as 1–3 d. Acclimation was associated with a change in the concentration of soluble sugars under controlled conditions, but not in the field. Our data suggest that acclimation in the field may be associated with the onset of cold‐induced photo‐inhibition. We conclude that cold‐acclimation of dark respiration in snow gum leaves is characterized by changes in both the temperature sensitivity and apparent ‘capacity’ of the respiratory apparatus, and that such changes will have an important impact on the carbon economy of snow gum plants.     

基于地形因素的高寒草甸土壤温湿度和物种多样性与初级生产力关系研究

山地是高寒草甸的主要分布区,地形变化引起了土壤温湿度和物种的差异性分布,进而影响到草地生态系统生产功能。为明晰高寒草甸山地环境因子(土壤温湿度)和物种多样性(丰富度、多度、均匀度、优势度)与初级生产力的关系,本研究以青藏高原东北缘马牙雪山支脉的高寒草甸山体为研究对象,选择阶地、阴坡、山脊和阳坡与3个海拔梯度段,调查了189个样方的植物群落组成和土壤温湿度。采用线性回归法分析土壤温湿度和物种多样性与初级生产力之间的关系。结果表明:(1)以山地高寒草甸整体为研究单元,初级生产力只随物种多度的增加而显著增加(R~2=0.07 P=0.01)。(2)坡向影响初级生产力的因素不同,阴坡初级生产力与物种丰富度正线性相关;山脊初级生产力与土壤湿度正线性相关,也随物种丰富度增加而显著增加;阳坡初级生产力与物种多度正线性相关;阶地初级生产力随均匀度增加而显著增加,随优势度增加而显著降低。(3)只有低海拔区(2860-2910 m)初级生产力随物种多度和丰富度的增加而显著增加。综上所述,山地高寒草甸土壤温湿度和物种多样性与初级生产力关系受坡向比海拔的影响更大,且物种多样性对初级生产力的影响大于土壤温湿度。建议山地高寒草甸生态系统生产和生态管理过程中要重点考虑坡向对植物多样性和初级生产力的影响。     

Plasma membrane fluidity and hydraulic conductance in wheat roots: interactions between root temperature and nitrate or phosphate deprivation

The hypothesis was tested that the negative effect of mineral nutrient deprivation (–N and –P) on the hydraulic conductance (L0) of wheat roots may be relieved by increasing the fluidity of plasma membrane (PM) lipids through elevated temperature. An increase in root temperature from 20 to 30°C increased the sap flow, J_v, from the excised roots of nutrient-deprived plants for 4 h, with a corresponding increase in L₀. In the same period, there was a decline in the flux of osmotically active solutes (J_s > to the xylem. As the duration of the period at 30°C increased, it was clear that the differential in L₀ between control and nutrient-deprived roots was maintained, even though L_u was significantly greater than the initial (20 °C) value after 48h. The lipid order parameter, determined by fluorescence polarization of 1, 6 diphenyl- 1, 3, 5-hexatriene (DPH), decreased markedly in two-phase purified PMs in the first 4 h of treatment at 30°C, but thereafter remained steady. The differential between control and nutrient-deprived roots was maintained throughout the 48h period. The correlation between lowered L₀ in nutrient-deprived roots and increased PM lipid ordering remained unchanged in conditions where the overall membrane fluidity was increased by elevated temperature.     

Community relaxation in fragmented landscapes: the relation between species richness, area and age

Estimates of species loss due to habitat destruction are normally based on calculations employing the species–area relation, S = cA ^z . The validity of this approach is based on the assumption that the value of the exponent ( z ) defining the slope of the species–area relation in nonfragmented communities is at a steady state and that z is thus a constant. However, departure from such an assumption renders this approach unreliable. Here I report the results from a natural field experiment using "model" bryophyte-based microlandscapes designed to follow the species richness dynamics of microarthropod communities postfragmentation. Community isolation due to fragmentation initiated a delayed community relaxation process and resulted in substantial local extinction. Over the period of the experiment z declined in the control communities and yet remained fairly stable in the fragmented communities. I conclude that predictions of species loss due to habitat fragmentation that do not take into account the fact that often z may not be a constant may lead to error-prone predictions of future species loss.     

Regulation of root respiration in two species of Plantago that differ in relative growth rate: the effect of short- and long-term changes in temperature

This study investigates the effect of short‐ and long‐term changesin temperature on the regulation of root respiratory O₂ uptakeby substrate supply, adenylate restriction and/or the capacityof the respiratory system. The species investigated were the lowland Plantagolanceolata L. and alpine Plantago euryphylla Briggs, Carolin& Pulley, which are inherently fast‐ and slow‐growing, respectively. Theplants were grown hydroponically in a controlled environment (constant23 °C). The effect of long‐term exposure to lowtemperature on regulation of respiration was also assessed in P.lanceolata using plants transferred to 15/10 °C(day/night) for 7 d. Exogenous glucose and uncoupler (CCCP)were used to assess the extent to which respiration rates were limitedby substrate supply and adenylates. The results suggest that adenylatesand/or substrate supply exert the greatest control overrespiration at moderate temperatures (e.g. 15–30 °C)in both species. At low temperatures (5–15 °C),CCCP and glucose had little effect on respiration, suggesting thatrespiration was limited by enzyme capacity alone. The Q₁₀ (proportionalincrease of respiration per 10 °C) of respirationwas increased following the addition of CCCP and/or exogenousglucose. The degree of stimulation by CCCP was considerably lowerin P. euryphylla than P. lanceolata. This suggeststhat respiration rates operate much closer to the maximum capacity in P.euryphylla than P. lanceolata. When P. lanceolata wastransferred to 15 °C for 7 d, respirationacclimated to the lower growth temperature (as demonstrated by an increasein respiration rates measured at 25 °C). In addition,the Q₁₀ was higher, and the stimulatory effectof exogenous glucose and CCCP lower, in the cold‐acclimated rootsin comparison with their warm‐grown counterparts. Acclimation of P.lanceolata to different day/night‐time temperatureregimes was also investigated. The low night‐time temperature wasfound to be the most important factor influencing acclimation. The Q₁₀ valueswere also higher in plants exposed to the lowest night‐time temperature.The results demonstrate that short‐ and long‐term changes in temperaturealter the importance of substrate supply, adenylates and capacityof respiratory enzymes in regulating respiratory flux.