Thorax Length Research Articles

Measurements of Eye size and Acuity in Aphids (Hemiptera: Aphididae)

(2): 077–084; Stuttgart 2009-07. – – – [Article]To locate suitable host plants herbivorous insects integrate information from several sensory mo-dalities. In this process, the visual sense is generally regarded to provide less specifi c information than olfaction or gustation, partly because of the relatively poor acuity of insect eyes. To investigate whether visual acuity increases with eye and body size in herbivorous insects, morphological eye features were measured in winged females of 20 aphid species of varied body size. The measurements included vertical eye length, ommatidial diameter, interommatidial angle, and number of ommatidia. Thorax length was measured as an indicator of body size. The insects were collected from fi eld sites in Great Britain and Germany and from laboratory cultures. All measurements were done digitally on pictures produced by a camera connected to a stereo microscope and a Personal Computer. Eye length (median 157 µm) and ommatidial diameter (median 10.1 µm) scaled positively with total thorax length, but the interommatidial angle (median 7.9°) and the number of ommatidia (median 214) did not, suggesting that larger aphid species do not invest in improving their visual acuity. The study shows that aphids, with their relatively few ommatidia and large interommatidial angles, have a comparatively low spatial resolution.

Post‐zygotic isolation in cactophilic Drosophila: larval viability and adult life‐history traits of D. mojavensis/D. arizonae hybrids

Drosophila mojavensis and Drosophila arizonae are cactophilic flies that have been used extensively in speciation studies. Incomplete premating isolation, evidence of reinforcement, and a lack of recent introgression between these species point to a potentially important role for post-zygotic isolating barriers in this system. Other than hybrid male sterility, however, post-zygotic isolation between D. mojavensis and D. arizonae has received little attention. In this study, we examined viability and life-history traits of D. mojavensis/D. arizonae F(1) hybrids from sympatric crosses. Specifically, we reared hybrids and purebreds on the natural host cacti of each parental species and compared viability, development time, thorax length, and desiccation resistance between hybrids and purebreds. Interestingly, hybrid females from both crosses performed similarly or even better than purebred females. In contrast, hybrid sons of D. arizonae mothers, in addition to being sterile, had shorter average thorax length than males of both parental species, and hybrid males from both crosses had substantially lower desiccation resistance than D. mojavensis males. The probable cost to hybridization for D. mojavensis females resulting from reduced desiccation resistance of hybrid sons may have been an important selective factor in the history of reinforcement for crosses involving these females.

Variations in morphological and life-history traits under extreme temperatures in Drosophila ananassae

Using half-sib analysis, we analysed the consequences of extreme rearing temperatures on genetic and phenotypic variations in the morphological and life-history traits of Drosophila ananassae. Paternal half-sib covariance contains a relatively small proportion of the epistatic variance and lacks the dominance variance and variance due to maternal effect, which provides more reliable estimates of additive genetic variance. Experiments were performed on a mass culture population of D. ananassae collected from Kanniyakumari (India). Two extremely stressful temperatures (18 degree C and 32 degree C) and one standard temperature (25 degree C) were used to examine the effect of stressful and non-stressful environments on the morphological and life-history traits in males and females. Mean values of various morphological traits differed signifi cantly among different temperature regimens in both males and females. Rearing at 18 degree C and 32 degree C resulted in decreased thorax length, wing-to-thorax (w/t) ratio, sternopleural bristle number, ovariole number, sex comb-tooth number and testis length. Phenotypic variances increased under stressful temperatures in comparison with non-stressful temperatures. Heritability and evolvability based on among-sires (males), among-dams (females), and the sum of the two components (sire + dam) showed higher values at both the stressful temperatures than at the non-stressful temperature. These differences reflect changes in additive genetic variance. Viability was greater at the high than the low extreme temperature. As viability is an indicator of stress, we can assume that stress was greater at 18 degree C than at 32 degree C in D. ananassae. The genetic variations for all the quantitative and life-history traits were higher at low temperature. Variation in sexual traits was more pronounced as compared with other morphometric traits, which shows that sexual traits are more prone to thermal stress. Our results agree with the hypothesis that genetic variation is increased in stressful environments.

Immune Function, Body Size, and Parasite Load in Lubber Grasshoppers

Immunity is an important biological property of organisms that protects them from parasites. Similarly, body size is one of the most important biological traits because almost all biological processes, from the cellular to the ecosystem level, scale with body size. Our goal was to determine the correlation between body size and immune function in different populations of the eastern lubber grasshopper (Romalea microptera) which differ in body size. Field data was collected on grasshopper location, size (thorax and femur lengths), and immune function (measured by melanization response). In accordance with previous work, we found a significant body size cline among populations of south Florida grasshoppers: on average, small adult grasshoppers are found in western populations whereas large grasshoppers are found in eastern populations. However, we did not find a significant relationship between body size and one measure of immune function, either within or across these populations. Future work should be directed at understanding when body size and immune function might or might not be correlated.

Quantitative morphometrical analysis of a North African population of Drosophila melanogaster: sexual dimorphism, and comparison with European populations

Genetic variability of quantitative traits was investigated in a Moroccan population of Drosophila melanogaster, with an isofemale line design. Results were compared with data previously obtained from French populations. Although the environmental and thermal conditions are very different in France and Morocco, only two significant differences were observed: a shorter wing and a lighter abdomen pigmentation in Morocco. It is, therefore, concluded that Moroccan D. melanogaster are quite typical temperate flies, belonging to the Palaearctic region, and very different from the ancestral Afrotropical populations. Almost all traits were genetically variable, as shown by significant intraclass correlations among lines. Genetic correlations were highly significant among three size-related traits, while much lower between size and bristle numbers. Fluctuating asymmetry was greater for abdominal bristles than for sternopleural bristles. Sex dimorphism, analysed as a female/male ratio, was identical in French and Moroccan populations. Examination of the thorax length/thorax width ratio showed that the thorax is more elongated in females. Sexual dimorphism of wing length was significantly more correlated to thorax width than to thorax length. The results illustrate the value of measuring numerous quantitative traits on the same flies for characterizing the genetic architecture of a natural population. In several cases, and especially for genetic correlations, some interesting suggestions could be made, which should be confirmed, or invalidated, by more extensive investigations.

Biology And Biometry Of A Beautiful And Forageable Freshwater Crustacean <i>Streptocephalus dichotomus</i> (Baird)

Crustaceans are the highly preferred delicacy for many organisms including man. The preference was reflected from the quantum of selective feed in take from the wild predatory organisms, which was evaluated by the gut content analysis. But the gut mainly contain partially digested or fragments of prey after digestion. Such a forage uptake could also used as a tool to quantify the actual consumption by the predators, in this regard the present work on length related parameter evaluation is mandatory. Hence, the relationship between length and other measurable body features (such as total length, total weight, head length, thorax length, abdomen length, cercopod length, male second antennal length and brood pouch length) were established here by measuring 118 males, 143 females and 54 juveniles of Streptocephalus dichotomus collected from the seasonal ponds at Bharathidasan University, Tamilnadu. The maximum size recorded was 42mm ♂ and 37 mm♀ indicating that males grow larger than females. The sexually dimorphic characters such as budding of the brood pouch in females and the predominantly larger second antenna occurred during 4th day from hatching at a size of 5mm length ♂. The first spawning was noted at the 11th day with a size of 9mm length. The body mean ‘Kn\' values coincide with the maturity stages and clutch periods. The results of the length related body measurements forms the basis in assessing its biomass from the gut content remnants of the predatory organism besides predicting the expected maturity size and quantum of cysts produced. The mean ‘Kn\' value in relation to weight was also calculated as a measure of its body condition during its growth phase. Further, Streptocephalus are able to complete their life cycle even in very small water bodies and in shorter duration of a fortnight. Keywords: Streptocephalus dichotomus, Length-weight relationship, Biometry, Fairy shrimpTropical Freshwater Biology Vol. 16 (2) 2007: pp. 35-43

Quantitative trait loci affecting phenotypic plasticity and the allometric relationship of ovariole number and thorax length in Drosophila melanogaster.

Environmental factors during juvenile growth such as temperature and nutrition have major effects on adult morphology and life-history traits. In Drosophila melanogaster, ovary size, measured as ovariole number, and body size, measured as thorax length, are developmentally plastic traits with respect to larval nutrition. Herein we investigated the genetic basis for plasticity of ovariole number and body size, as well the genetic basis for their allometric relationship using recombinant inbred lines (RILs) derived from a natural population in Winters, California. We reared 196 RILs in four yeast concentrations and measured ovariole number and body size. The genetic correlation between ovariole number and thorax length was positive, but the strength of this correlation decreased with increasing yeast concentration. Genetic variation and genotype-by-environment (G x E) interactions were observed for both traits. We identified quantitative trait loci (QTL), epistatic, QTL-by-environment, and epistatic-by-environment interactions for both traits and their scaling relationships. The results are discussed in the context of multivariate trait evolution.

Genetic evidence for cohort splitting in the merovoltine stonefly Pteronarcys californica (Newport) in Blacksmith Fork, Utah

The life cycles of many stream insects results in the simultaneous existence of multiple cohorts within populations. If larval development is fixed in these long-lived species, successive cohorts may be reproductively isolated and genetically distinct. We examined levels of genetic differentiation in a 333 bp region of the mitochondrial cytochrome-b gene among cohorts of the stonefly Pteronarcys californica (Newport) (Plecoptera, Pteronarcyidae) at two sites along Blacksmith Fork, Utah. Body measurements were collected from 224 specimens. The frequency distribution of (head width) X (head + thorax length) suggests four (Low site) and five year (High site) life cycles comprising an ∼one year embryonic diapause followed by either three or four years of larval development. Seventy-seven individuals were sequenced, from which we detected five unique mtDNA haplotypes. The overall AMOVA suggested moderate genetic differentiation among cohorts (F ST = 0.11, p = 0.01; ΦST = 0.11, p = 0.007). However, pairwise analyses indicated that a single cohort drove the overall ΦST value. Thus, we conclude that there is considerable gene flow among most cohorts of P. californica in Blacksmith Fork.

Effects of Phenotype and B-Chromosomes on Adult Survival in Dichroplus elongatus (Orthoptera: Acrididae)

The grasshopper Dichroplus elongatus Giglio Toss is an example of a species with widespread B-chromosome polymorphism. We detected in males considerable variation in adult size, and part of this variation is associated with the polymorphism for B-chromosomes that has a negative effect on male body size. The analysis of fitness components revealed that B-carriers are negatively selected during mating, whereas B-carrier females exhibited higher fecundity than standard females. We recorded adult survival in relation to karyotype and body size, as measured by total, third tibia, third femur, thorax, and tegmen lengths. Our data showed directional phenotypic selection favoring large males and, as expected from the relationship between karyotype and phenotype, chromosome directional selection was detected favoring males with standard karyotype. In females, the effects of phenotype on survival showed an opposite tendency to that detected in males, i.e., small females outlive large females. Phenotypic selection in females may be explained by a trade-off between early and late fitness components. Our results suggest that B-chromosomes cause detrimental effects on body-size related traits that are selected for adult male survival. All available information on B-chromosomes in D. elongatus supports the hypothesis that their persistence in Argentinean populations depends on trade-offs between opposite selective effects.

Effects of Phenotype and B-Chromosomes on Adult Survival in <I>Dichroplus elongatus</I> (Orthoptera: Acrididae)

The grasshopper Dichroplus elongatus Giglio Toss is an example of a species with widespread B-chromosome polymorphism. We detected in males considerable variation in adult size, and part of this variation is associated with the polymorphism for B-chromosomes that has a negative effect on male body size. The analysis of fitness components revealed that B-carriers are negatively selected during mating, whereas B-carrier females exhibited higher fecundity than standard females. We recorded adult survival in relation to karyotype and body size, as measured by total, third tibia, third femur, thorax, and tegmen lengths. Our data showed directional phenotypic selection favoring large males and, as expected from the relationship between karyotype and phenotype, chromosome directional selection was detected favoring males with standard karyotype. In females, the effects of phenotype on survival showed an opposite tendency to that detected in males, i.e., small females outlive large females. Phenotypic selection in females may be explained by a trade-off between early and late fitness components. Our results suggest that B-chromosomes cause detrimental effects on body-size related traits that are selected for adult male survival. All available information on B-chromosomes in D. elongatus supports the hypothesis that their persistence in Argentinean populations depends on trade-offs between opposite selective effects.

Spartan defense in the Thermopylae pass: Strategic defense by aggregations of Pseudomyrmex spinicola (Hymenoptera, Formicidae) on the trunk of Acacia collinsii (Mimosaceae)

Acacia ants (Pseudomyrmex spinicola) usually prune all of the vegetation growing in the vicinity of their host plant (Acacia collinsii). This lack of branches in contact with the host tree makes the main stem of the acacia the only point of access for ants invading the resident colony. The present study assessed whether the intrusion site affects the probability of the intruder being detected. It also investigated whether ants that remain inactive on the main trunk base (a) are involved in defensive duties and (b) are morphologically different from other colony members (e.g. foraging ants). In the field, intruder ants were placed on the trunk and leaves of acacias inhabited by P. spinicola; colony members on the trunk base and the leaves were marked and monitored; and head length, head width, and thorax length of ants that were either foraging on the leaves or immobile on the trunk were measured. P. spinicola ants found intruder ants entering their host acacia via the trunk more rapidly than those entering by means of the leaves. Ants on the base of the trunk do not exchange tasks with foragers: between 5 and 47% of the 1063 ants originally marked on the trunk were re-observed there, whereas only two of the 804 ants marked on the leaves were seen on the trunk. However, ants on the trunk were similar to foragers in morphology, suggesting that defensive ants may be part of a behavioral caste.

Emergent body size of mayfly survivors

Summary1. Employing field‐deployed mesocosms, we examined the effects of 12‐h pulse and 20‐day press (continuous) exposures of the common agricultural insecticide, imidacloprid, on nymph abundance, emergence patterns and adult body size of Epeorus spp. (Heptageniidae) and Baetis spp. (Baetidae).2. In press exposures, reduced nymph density was driven by reduced survivorship; in pulse exposures, reduced nymph density may reflect increased emergence because of stress.3. Once exposed to imidacloprid, Epeorus and Baetis mayflies developed less and emerged smaller than their control counterparts. Concentrations as low as 0.1 μg L−1 (12‐h pulse) reduced head length in Baetis and thorax length in Epeorus.4. In all of the Baetis and Epeorus examined, effects were only found in males. Male survivorship and body size can affect population dynamics. Sublethal doses of this widely applied agricultural insecticide have the potential to reduce reproductive success of mayfly populations.

Effect of developmental temperature stress on fluctuating asymmetry in certain morphological traits in Drosophila ananassae

In the present study, the effect of thermal stress on the variability and fluctuating asymmetry (FA) in different morphological traits, viz., thorax length (TL), sternopleural bristle number (SBN), wing length (WL), wing-to-thorax (W/T) ratio, sex comb tooth number (SCTN) and ovariole number (ON), was investigated in 10 isofemale lines of Drosophila ananassae. The phenotypic and genetic variability is higher in the flies reared at low (20 °C) and at high (30 °C) temperatures as compared to that of standard (25 °C) temperature. Further, the levels of FA of measured traits differed significantly among the three temperature regimes except SBN and SCTN in males and SBN and W/T ratio in females. Moreover, the magnitude of positional fluctuating asymmetry is similar in males reared at three different developmental temperatures for SBN and SCTN but it varies significantly for SBN in females. However, when FA across all the traits was combined into a composite index (CFA), significant differences were found for both temperature regimes and sexes. Males showed higher CFA at 30 °C whereas in females it was higher at 20 °C. The results suggest that temperature increases the levels of variability and FA but the effect seems to be trait and sex specific in D. ananassae.

Antagonistic selection between adult thorax and wing size in field released Drosophila melanogaster independent of thermal conditions

Attempts to explain size variation in Drosophila and other small insects often focus on the larval stage and association between development time and size, but patterns are also influenced by direct selection on size-related traits in the adults. Here we use multiple field releases of Drosophila melanogaster to test the association between size and one component of field fitness, the ability of Drosophila to locate resources for feeding and breeding. We find antagonistic selection between wing length and thorax length in both males and females, such that capture at baits is higher for flies with relatively larger thorax lengths and smaller wings. However flies with large wings relative to thoraces disperse further as reflected in the longer distances moved to baits. These patterns did not depend strongly on weather conditions, suggesting that selection on adult size is at least partly independent of temperature. Antagonistic selection between size traits can generate changes in size along gradients if the distribution of resources in the environment varies and selects for different dispersal patterns, particularly as dispersal is relatively higher under warmer conditions.

Evolutionary genetics of Drosophila ananassae: evidence for trade-offs among several fitness traits

Correlated responses to bi-directional selection on thorax length, examined on several life-history traits and chromosome inversion polymorphisms, have revealed apparent novel trade-offs in Drosophila ananassae. We provide evidence of trade-offs between hatching time and pupal period, pupal period and egg-pupa development time, and pupal period and larval development time (LDT). Body size shows positive correlations with ovariole number, LDT and DT (egg–fly). We provide evidence of sexual dimorphism for trade-offs between longevity and body size and starvation and longevity in females only. Trade-offs between wing/thorax (W/T) ratio and longevity, W/T ratio and starvation, and DT (egg- fly) and longevity are evident in males only. Sexual dimorphism is also evident for inversion polymorphism with body size and longevity. A longevity assay suggests that low line females outlived high line females whereas high line males outlived low line males. The mean longevity in males is negatively correlated with the 2L-ST and 3R-ST arrangement frequencies whereas the 3L-ST arrangement frequency is positively correlated with the mean longevity in males but opposite arrangements are found in females. Absolute starvation resistance is negatively correlated with 2L-ST and 3R-ST chromosome arrangements and results in a trade-off between longevity and absolute starvation resistance in females. Analyses of fecundity, hatchability, and viabilities based on age intervals in both G10 and G13 suggest that the early reproduction is favoured in D. ananassae. The productivity percentage is highest in the high line and there is no effect of late reproduction on it. Overall, we provide some unravelled trade-offs and striking sex differences, which may help in understanding the life-history evolution of the species. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90, 669–685.

SEXUAL SELECTION ON MULTIVARIATE PHENOTYPES IN ANASTREPHA FRATERCULUS (DIPTERA: TEPHRITIDAE) FROM ARGENTINA

Despite the interest in applying environmentally friendly control methods such as sterile insect technique (SIT) against Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae), information about its biology, taxonomy, and behavior is still insufficient. To increase this information, the present study aims to evaluate the performance of wild flies under field cage conditions through the study of sexual competitiveness among males (sexual selection). A wild population from Horco Molle, Tucumán, Argentina was sampled. Mature virgin males and females were released into outdoor field cages to compete for mating. Morphometric analyses were applied to determine the relationship between the multivariate phenotype and copulatory success. Successful and unsuccessful males were measured for 8 traits: head width (HW), face width (FW), eye length (EL), thorax length (THL), wing length (WL), wing width (WW), femur length (FL), and tibia length (TIL). Combinations of different multivariate statistical methods and graphical analyses were used to evaluate sexual selection on male phenotype. The results indicated that wing width and thorax length would be the most probable targets of sexual selection. They describe a nonlinear association between expected fitness and each of these 2 traits. This nonlinear relation suggests that observed selection could maintain the diversity related to body size.

Predator foolhardiness and morphological evolution in 17-year cicadas (Magicicada spp.)

Periodical cicadas in the genus Magicicada have an unusual life history that includes an exceptionally long life cycle and a massive, synchronized emergence. Considerable effort has been put into research aimed at understanding the evolutionary history of periodical cicadas, but surprisingly little attention has been given to their morphological evolution. Their slow flight and approachability have been described as ‘predator-foolhardy’ behaviour. We quantified flight speeds for M. cassini, M. septendecim, and Tibicen chloromera (a nonperiodical cicada species), and interpreted them in terms of thorax musculature, body proportions and wing size and shape in relation to body size. On average, T. chloromera flew three to four times faster than did the two Magicicada species. Using empirical relationships between flight speed and body length, body mass or wing loading, we determined M. cassini and M. septendecim to be unusually slow fliers for their body size, whereas T. chloromera was not. The relatively slow flight speeds of Magicicada species could be largely accounted for by relatively small thoracic muscle masses, as indicated by thorax length × width measurements, and low wing loadings. Aspect ratio differences were contributing factors. Male Magicicada and female Tibicen were more active in mate searching than was the opposite sex, and correspondingly had relatively large aspect ratios. We interpret the morphological traits responsible for the slow flight of Magicicada species as being adaptations to searching for mates in dense aggregations around the canopy of trees, relatively unconstrained by the per-capita risk of predation. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90, 1–13.

Effects of B chromosomes and supernumerary segments on morphometric traits and adult fitness components in the grasshopper, Dichroplus elongatus (Acrididae)

The South American species, Dichroplus elongatus, is polymorphic for B chromosomes and supernumerary segments in chromosome pairs M6 (SS6), S9 (SS9) and S10 (SS10). Both forms of supernumerary heterochromatin shape chiasma frequency and distribution and B chromosomes also affect male fertility. Here, we analysed the effects of these polymorphisms on morphometric traits (total, 3rd femur, 3rd tibia, thorax and tegmen lengths) and several adult fitness components, including male and female mating success, and female reproductive potential. B chromosomes tend to decrease, and SS6 segments to increase the body size of carriers. The analysis of reproductive potential suggested that B chromosome carrying females have higher numbers of embryos per clutch and ovarioles per ovary. The uni- and multivariate analysis of mating success revealed that sexual selection favours larger individuals of both sexes and males with standard karyotype. B chromosomes may have accumulation mechanisms, which involve preferential transmission of B chromosomes to germ cells or functional gametes. The maintenance of Bs might be explained by interactions among accumulation mechanisms and trade-offs between detrimental and favourable effects on different fitness components.

Multivariate selection for the rest of us

Multivariate selection for the rest of us

Sexual size dimorphism in a Drosophila clade, the D. obscura group

The Drosophila obscura clade consists of about 41 species, of which 20 were used for analyses of wing and thorax length. Our primary goal was to investigate the magnitude of sexual size dimorphism (SSD) of these traits within this clade and to test Rensch's Rule [when females are larger than males, SSD (e.g., female/male ratio) should decrease with body size]. Our secondary goal was methodological and involved evaluating for these flies alternative measures of SSD (female/male ratio, female/male absolute difference, female/male relative difference), developing a bootstrap method to estimate the magnitude of intraspecific variation in SSD, and applying a new method of estimating allometric relationships that is phylogenetically based and incorporates error variance in both traits. All indices of SSD were strongly correlated for both size traits. Nevertheless, female/male ratio is the best index here: it is easily interpretable and essentially independent of size. For both traits, SSD (F/M) varied interspecifically, showed a strong phylogenetic signal, but did not differ for the main phylogenetic subgroups or correlate with latitude. Factors underlying variation in SSD in this clade are elusive and might include genetic drift. SSD (wing) tended to decrease with increasing size, as predicted by Rensch's Rule, though not consistently so. SSD (thorax) was unrelated to size. However, analysis of published data for thorax length of Drosophila spp. ( N=42) with a larger size range showed that SSD decreased significantly with increasing size (consistent with Rensch's Rule), suggesting our ability to detect SSD-size relations in the D. obscura data may be limited by low statistical power.