Distinct Body Size Research Articles

Niche filling predicts evolutionary trajectories in insular bird communities

Abstract Different theories have been proposed to explain the phenotypic changes observed in island lineages, but it remains unclear if predictable evolutionary trajectories can be identified within island communities. Using a 3D functional space approach, we tested whether insular endemic species tend to evolve towards apparent holes in niche space (expecting niche filling) or tend to become generalists, that is, moving towards the centre of the functional space (expecting niche expansion). We tested these two hypotheses in 378 insular endemic species from 24 islands of 8 archipelagos, including 177 prehistoric anthropogenically extinct species. Analyses were conducted with and without accounting for species size difference. We found that 57% of island endemic species evolved towards more unoccupied regions of the global morphospace (i.e. more distinct body sizes compared to the ones of their ancestors), suggesting a tendency for niche filling. When adjusted traits for body size, we found that half of the endemic species (50%) showed more distinct trait values than their ancestors. Results also revealed that certain dietary niches (terrestrial herbivores and nectarivores) evolved distinct body sizes more frequently. Differences noted between islands and archipelagos suggest that biogeographic factors may influence evolutionary trajectory and interactions between these two hypotheses. Our study confirms that extinct species occupied specific niches that have been left vacant, suggesting that these evolutionary ‘oddities’ could be more sensitive to extinction. Overall, it calls for a global assessment of the avian functional diversity lost from recent extinctions. Read the free Plain Language Summary for this article on the Journal blog.

Exploring mechanisms of spatial segregation between body size groups within fish populations under environmental change

Ample evidence has indicated shifts in distribution of fish populations in response to environmental stress. However, most studies focused at the whole population scale. This neglects the spatial dynamics between groups of different body size (body size groups), that fundamentally shapes the spatial structure of a population. Here, we explored the mechanisms that modulate spatial dynamics of body size groups, and applied our analyses to three North Sea fish populations which experienced severe declines in biomass from 1977 to 2019: Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangius. All three populations exhibited strong declines in the overlapped area between body size groups in winter over 43 years, yet their mechanisms differed. These declines were either due to 1) different magnitudes of contraction of the distribution area of body size groups; and/or 2) different speeds and directions of spatial shift among various body size groups, both increasing spatial segregation within populations. These patterns were either associated with ocean warming, and/or declining population biomass, and such associations often varied according to distinct body size groups. Increasing spatial segregation between size groups of a population likely hampers life‐cycle connectivity and stability to local perturbations. Our analytical approach provides a powerful tool for identifying vulnerable populations under environmental stress and can be generalized to study a variety of size/age structured populations at various ecosystem types.

Body size as a proxy of probing time and visitation rates on cucumber by two African stingless bees increase fruit quality and seed quantity

Pollinators are of essential importance for sustainable agriculture. However, pollination efficiency depends on interacting factors such as pollinator behaviour and morphology. We compared the effect of probing time length and visit frequency of two distinct body size African stingless bee species (Meliponula bocandei, Dactylurina schmidti) as alternative pollinators to Apis mellifera scutellata on greenhouse cultivated cucumber. We found differences in morphometric characteristics, between a set of 9 body parameters. Bee body size was the morphological feature that varied the most among bee species. On average, body size was largest in honeybees, followed by M. bocandei, and finally D. schmidti, which was the smallest. Glossa length was different between the bee species: A. mellifera scutellata (2.86 ± 0.026 mm), M. bocandei (2.20 ± 0.031 mm), D. schmidti (0.72 ± 0.025 mm). Such differences among bee species in body parameters correspondingly affected nectar probing times during a single flower visit, which were different for the bee species. D. schmidti (3.34 ± 0.56 s) had the longest probing time, while M. bocandei (2.57 s) had the shortest. Fruit quality was strongly positively influenced by the visit duration during a single visit on female flowers. The slope of fruit quality produced was higher in flowers pollinated by M. bocandei. During a single flower visit, heavier and bigger fruits were obtained in the gold standard hand cross pollination and flowers pollinated by M. bocandei. The bee species and the number of visits significantly impacted fruit weight, fruit volume and number of seeds. Subsequent visit performed by M. bocandei positively impacted fruit quality. Three visits on a flower were enough to ensure the production of high-quality fruits. Fruit sweetness depended on the number of visits received by the flower, but not on the bee species that performed the visit. Altogether, our results indicate that the stingless bees M. bocandei is more an efficient pollinator of cucumber than A. m. scutellata and D. schmidti and can be recommended for use under greenhouse cultivation.

Bacteria versus fungi for predicting anthropogenic pollution in subtropical coastal sediments: Assembly process and environmental response

Coastal regions support the most threatened ecosystems on Earth, and anthropogenic activities have been significantly affecting both habitat structure and ecological quality. Understanding the dynamics of ecological response to multiple stresses is a precondition for management and restoration of largely disturbed coastal ecosystems. Among diverse taxa in coastal regions, benthic organisms are widely recognized as promising targets for assessing ecological causes and consequences of anthropogenic activity-derived stressors, such as environmental pollution. However, spatial and local environmental factors play important but different roles in shaping community structure of different benthic taxa, mainly owing to their distinct body size, mobility, and metabolic capacity. Here, we applied metabarcoding, coupled with physicochemical analyses, to determine the benthic microbial community composition in a typical subtropical coast area, Beibu Gulf in Southern China. Stochastic processes were found as the dominant ecological driver in shaping the community assembly of both bacteria and fungi. Moreover, environmental factors explained a considerable portion of variation in bacterial communities, while spatial factors were more influential in structuring larger body size and weak mobility fungal communities. Mantel tests and network analysis revealed significant relationships between several environmental variables and bacterial communities. More importantly, the concentrations of heavy metals, particularly Cr and Zn, could be predicted using the constructed random forest model based on bacterial communities. The results obtained here provide new insights into causes and consequences of various factors for influencing healthy coasts, thus further clearing the road to the integration of biological information into routine ecological monitoring of coastal ecosystems.

Uncovering men’s stereotype content (warmth and competence) associated with a representative range of male body size categories

Research indicates that 40 % of men experience weight-related stigmatization. Yet perceptions of body size continue to be understudied in men and the stereotype content of men’s weight status remains largely unknown. Grounded in Stereotype Content Model, the research aims to uncover men’s stereotype content associated with distinct body sizes. A pilot study tested the methodological design using a representative measure of BMI-specific images among a sample of undergraduate men (N = 80). Study 1 included the BMI-specific images to assess stereotype content among a broad online sample (N = 142) and explored how participant BMI relates to such perceptions. Study 2 included images of real men to increase the ecological validity of our findings (N = 152). We also included empathy and protestant ethics to examine possible interaction effects. Results revealed that normal to overweight men scored highest on warmth and competence, while underweight and obese classes were perceived less favorably and, evidently, stereotype perceptions were increasingly severe with adiposity. Empathy moderated evaluations of warmth toward stigmatized groups, and protestant ethics moderated warmth appraisals for underweight and normal weight targets but did not influence perceptions of competence. Overall, weight stereotype content should be considered when understanding stigma-related experiences in men.

Scale‐dependent patterns of metacommunity structuring in aquatic organisms across floodplain systems

AbstractAimEvaluating how groups of organisms vary in dispersal capability and how environmental, spatial and temporal signals vary across multiple scales is critical to elucidating metacommunity theory. We examined whether the relative contributions of environmental, spatial and hydrological factors have different effects on organismal groups with different dispersal abilities at three spatial scales, and how this knowledge contributes to our understanding of metacommunity dynamics.LocationFour major Brazilian floodplains, with the largest distance among them of 2,300 Km.Taxon10 aquatic organismal groups, ranging from bacterioplankton to fish.MethodsWe sampled lakes connected to the main river in the low‐ and high‐water periods of each floodplain between 2011 and 2012. Different biological groups were analysed across three hierarchical spatial scales (fine, intermediate and subcontinental) within and between floodplain systems. We applied a series of partial redundancy analyses to estimate the relative contributions of environmental factors, spatial factors and hydrological period for each biological group.ResultsAt the fine spatial scale, predominantly environmental factors and hydrological period structure metacommunities, although less so for microorganisms than for micro‐invertebrates and macro‐organisms. The relative importance of environmental factors increased at the intermediate spatial scale. At the subcontinental scale, the relative importance of spatial factors increased for all biological groups, but environmental factors remained the primary regulators of microorganisms even at the largest scale.Main conclusionsThis study design allowed us to make more robust inferences about the mechanisms responsible for regulating community structure of distinct biological groups at different spatial scales. Our results suggest that biological groups displaying distinct body size likely determine the spatial extent at which environmental, spatial and hydrological processes prevail as the primary regulators of community structure. These findings are important in guiding the conservation and management of floodplain biodiversity because these systems are naturally highly heterogeneous in space and time.

Ecological preferences of the endemic reptile community of Socotra

The Socotra Archipelago is a unique hotspot of biodiversity, particularly for terrestrial reptiles (28 endemic out of 31 native species) whose ecology is known only in general terms. We describe the ecological preference and the daily activity of 21 species of terrestrial reptiles, geckos, lizards, skinks, snakes and chameleon, from the largest island of the archipelago. The database includes 6950 records collected by 260 standardized transects from 2007 to 2013. The sister species Haemodracon riebeckii–H. trachyrhinus with very distinct body sizes, overlapped in their distribution but segregated by habitat and substrate. Three pairs of sister species with great phylogenetic affinity and similar morphology (Pristurus insignis–P. insignoides; Pristurus guichardi–P. obsti; Hemidactylus dracaenacolus–H. granti) were only partially segregated by distribution, habitat, substrate and body size, in the order of decreasing frequency. On the contrary, the other, phylogenetically more distant species of geckos, widely distributed and less similar in morphology, overlapped completely in their habitat use and distributional range. Such patterns suggest that strictly related species reduced their competition by segregation in different habitats and temporal niches and by non-overlapping distribution within the relatively small island of Socotra. On the other hand, the activity rhythm was similar within each genus. The unique biodiversity of Socotra endured up to present, thanks to a human impact lower than for most other inhabited islands, but the pace of change has accelerated recently. Conservation measures are urgent, particularly for the species of endemic geckos with a distribution range as small as 10 km2.

Biological Studies of the Oligonychus litchii (Trombidiformes:Tetranychidae) on Four Commercial Litchi Cultivars

Litchi is one of the most important pillars of the fruit industry in Southeast Asia and mainland China. The litchi spider mite, Oligonychus litchii Lo & Ho (Prostigmata: Tetranychidae), is a major pest of litchi. To determine the influence of different litchi cultivars on the life cycle, fecundity, and longevity of O. litchii, life tables of O. litchii on 4 popular commercial litchi cultivars in China (‘Baili,’‘Fezixiao,’‘Sanyuehong,’ and‘Nuomici’) were constructed under laboratory conditions at 25 ± 1 °C, 65 to 80% RH, and photoperiod of 14: 10 h (L: D). Life stages of O. litchii consist of egg, larva, protonymph, deutonymph, and adult, with distinct body sizes and colors. The life table parameters were significantly influenced by litchi cultivars. Our results showed that the developmental time of immature O. litchii was significantly longer on Baili than on the other 3 litchi cultivars. The immature survival rates of O. litchii varied from 21.74% to 68.42%. Oligonychus litchii laid significantly more eggs on Nuomici (64.84 eggs per female) than on other cultivars. The population doubling time of O. litchii ranged from 4.56 to 22.42 d, and a significant varietal effect was seen. The mites feeding on Nuomici showed the lowest intrinsic rate of natural increase per d (rm = 0.14 female per female per d). In addition, the net reproductive rate (R0) and finite rate of increase (λ) of O. litchii had the highest value on Nuomici (22.86 female per female per generation, and 1.16 female per female per d, respectively). The comparison of rm, R0, and immature survival rate of O. litchii on host plants revealed that Nuomici is the most suitable cultivar, suggesting that Nuomici is more susceptible to the litchi spider mite than the other 3 litchi cultivars.

Relationship of Circulating Fetuin-A Levels with Body Size and Metabolic Phenotypes.

Background Previous studies have suggested the existence of distinct body size subgroups according to metabolic health referred to as metabolically healthy obesity (MHO) and metabolically abnormal but normal weight (MANW) patients. Although nonalcoholic fatty liver disease (NAFLD) is strongly associated with obesity and metabolic syndrome, the relationship between these phenotypes and fetuin-A, a representative hepatokine, has not been explored. Methods We examined the association between circulating fetuin-A levels, metabolic health phenotypes, cardiometabolic risk parameters, and subclinical atherosclerosis in 290 subjects who were randomly selected from an ongoing cohort study. Results Fetuin-A concentrations were significantly associated with detrimental anthropometric and laboratory measurements, including increased waist circumference, blood pressure, alanine aminotransferase, fasting plasma glucose, and triglyceride levels. Furthermore, fetuin-A levels were significantly increased in the metabolically abnormal (MA) group compared to the metabolically healthy (MH) group in subjects without obesity (717.1 [632.1, 769.7] vs. 599.5 [502.0, 709.3], P = 0.001) and subjects with obesity (704.1 [595.5-880.9] vs. 612.2 [547.9-802.1], P = 0.016). In addition, brachial-ankle pulse wave velocity (baPWV), which reflects arterial stiffness, was higher in MA individuals compared to MH individuals. Multiple logistic regression analysis revealed that both individuals without obesity (P for trend = 0.017) and with obesity (P for trend = 0.028) in the higher tertiles of fetuin-A had an increased risk of MA than those in the lowest tertile. Conclusions This study demonstrates that fetuin-A levels are significantly associated with metabolic health phenotypes, such as MHO and MANW, in Korean adults.

Large herbivores influence plant litter decomposition by altering soil properties and plant quality in a meadow steppe

Large herbivores act as a major driver of plant litter decomposition in grasslands. The modifications of soil biotic and abiotic properties, as well as the changes in quality (C/N ratio) of plant litter, are two key pathways by which large herbivores can affect litter decomposition. Yet we know little about the relative role of these two mechanisms in mediating decomposition. Here, by combining a large-scale and a small-scale field manipulative experiment, we examined how livestock (cattle and sheep) grazing affects standing litter decomposition of a dominant grass, Leymus chinensis in grasslands in northeast China. We found that livestock grazing affected litter decay rate both by its influences on soil property (soil moisture, nutrient content, and microbial communities) and on plant litter quality (C/N ratio). Due to their distinct body size and diet preference, cattle and sheep affected soil property and litter quality, thus litter decay rate, differently by causing varying disturbance regimes and by feeding on different dominant species. Our study provides evidence that herbivore grazing can influence litter decomposition by modifying soil conditions and litter quality independently. Therefore, choosing the proper large herbivore(s) in grazing regimes may be important in maintaining nutrient cycling in grassland ecosystems.

The effects of land use change on native dung beetle diversity and function in Australia's Wet Tropics

The impacts of land use change on biodiversity and ecosystem functions are variable, particularly in fragmented tropical rainforest systems with high diversity. Dung beetles (Scarabaeinae) are an ideal group to investigate the relationship between land use change, diversity and ecosystem function as they are easily surveyed, sensitive to habitat modification and perform many ecosystem functions. Although this relationship has been investigated for dung beetles in some tropical regions, there has been no study assessing how native dung beetles in Australia's tropical rainforests respond to deforestation, and what the corresponding consequences are for dung removal (a key ecosystem function fulfilled by dung beetles). In this study we investigated the relationship between dung beetle community attributes (determined through trapping) and function (using dung removal experiments that allowed different dung beetle functional groups to access the dung) in rainforest and cleared pasture in a tropical landscape in Australia's Wet Tropics. Species richness, abundance and biomass were higher in rainforest compared to adjacent pasture, and species composition between these land use types differed significantly. However, average body size and evenness in body size were higher in pasture than in rainforest. Dung removal was higher in rainforest than in pasture when both functional groups or tunnelers only could access the dung. Increased dung removal in the rainforest was explained by higher biodiversity and dominance of a small number of species with distinct body sizes, as dung removal was best predicted by the evenness in body size of the community. Our findings suggest that functional traits (including body size and dung relocation behaviour) present in a dung beetle community are key drivers of dung removal. Overall, our results show that deforestation has reduced native dung beetle diversity in Australian tropical landscapes, which negatively impacts on the capacity for dung removal by dung beetles in this region.

Combined effects of calcium deficiency, cyanobacteria, and warming on the population fitness of three cladocerans

Aqueous calcium decline is a novel and widespread threat to soft-water lakes and usually co-occurs with other stressors. A three-way full factorial design was used to investigate the combined effects of a chemical stressor (calcium decline from 20 to 5 mg L -1 ), a biological stressor (50 % Microcystis aeruginosa in diets), and a physical stressor (temperature increase from 25 to 29 °C) on the population fitness of three common cladocerans with distinct body sizes. Both Ca deficiency and increasing cyanobacteria significantly depressed fitness in the large-bodied Daphnia pulex, while warming did not. The combined effect of Ca deficiency and increasing cyano- bacteria was significantly synergistic in D. pulex with a greater fitness reduction in the presence of cyanobacteria. Ca deficiency significantly depressed Simocephalus vetulus fitness only at 29 °C. Ca deficiency and warming had a synergistic effect on S. vetulus fitness, but the combined effect of warming and cyanobacteria was antagonistic. The fitness of the small-bodied B. longirostris increased with temperature, but was not influenced by Ca deficiency, cyanobacteria, or the interactions of the three stressors. These results suggest that D. pulex was most vulnerable to ongoing Ca decline. The non-additive effects of multiple stressors should be considered when predicting zooplank- ton responses in soft-water lakes.

SIZE-DEPENDENT MORTALITY AND COMPETITION INTERACTIVELY SHAPE COMMUNITY DIVERSITY

Body size is recognized as a major factor in evolutionary processes mediating sympatric diversification and community structuring. Life-history types with distinct body sizes can result from two fundamental mechanisms, size-dependent competition and size-dependent mortality. While previous theoretical studies investigated these two processes in separation, the model analyzed here allows both selective forces to affect body-size evolution interactively. Here we show for the first time that in the presence of size-dependent competition, size-dependent mortality can give rise to multiple, coexisting size morphs representing the final outcomes of evolution. Moreover, our results demonstrate that interactions between size-dependent competition and mortality can create characteristic abrupt changes in size structure and nonmonotonic patterns of biological diversity along continuous and monotonic environmental gradients. We find that the two selective forces differentially affect the body-size ratios of coexisting morphs: size-dependent competition results in small and relatively constant ratios, whereas size-dependent mortality can open niches for morphs that greatly differ in body size. We show that these differential effects result in characteristic distributions of size ratios across communities, which we suggest can help detect the concurrent action and relative influence of size-dependent competition and mortality in nature.

On the evolution of shape and size divergence in Nebria (Nebriola) ground beetles (Coleoptera, Carabidae)

Ground beetles include many species of rather recent evolutionary origin that are extremely similar in their external morphology. We used geometric morphometrics to quantify the relative degree of morphological divergence in three closely related polytypic alpine species of the genus Nebria, subgenus Nebriola (Nebria cordicollis, N. laticollis and N. fontinalis). To examine evolutionary patterns, we adopted a hierarchical design, using both shape and size to discriminate between species, subspecies within species, and populations within subspecies. A semilandmark-based approach was used to describe the pronotum, elytron and median lobe of the aedeagus. The three closely related species diverged significantly in shape and size. There were clear interspecific differences in the shape of external traits (elytron and pronotum) and of the median lobe of the aedeagus. Furthermore, species also diverged in body size, and in the relative size of traits (evaluated by computation of their static allometries). Shape differences among subspecies and populations were more limited. However, the three subspecies of N. cordicollis considered, N. c. cordicollis, N. c. kochi and N. c. winkleri, showed three distinct body sizes and differences in relative size of the elytron. A few size differences were also evident between distinct populations. These results seem to suggest that size may diverge more rapidly than shape in Nebriola ground beetles. Both at the species and subspecies level, body size order was not reflected in the relative size order, indicating that body size and relative size of traits do not necessarily evolve in concert.

Fight versus flight: the interaction of temperature and body size determines antipredator behaviour in tegu lizards

Ectotherm antipredator behaviour might be strongly affected both by body temperature and size: when environmental temperatures do not favour maximal locomotor performance, large individuals may confront predators, whereas small animals may flee, simply because they have no other option. However, integration of body size and temperature effects is rarely approached in the study of antipredator behaviour in vertebrate ectotherms. In the present study we investigated whether temperature affects antipredator responses of tegu lizards, Tupinambis merianae, with distinct body sizes, testing the hypothesis that small tegus (juveniles) run away from predators regardless of the environmental temperature, because defensive aggression may not be an effective predator deterrent, whereas adults, which are larger, use aggressive defence at low temperatures, when running performance might be suboptimal. We recorded responses of juvenile (= small) and adult (= large) tegu lizards to a simulated predatory attack at five environmental temperatures in the laboratory. Most differences between the two size classes were observed at low temperatures: large tegus were more aggressive overall than were small tegus at all temperatures tested, but at lower temperatures, the small lizards often used escape responses whereas the large ones either adopted a defensive posture or remained inactive. These results provide strong evidence that body size and temperature affect the antipredator responses of vertebrate ectotherms. We discuss the complex and intricate network of evolutionary and ecological parameters that are likely to be involved in the evolution of such interactions.

Origination and extinction patterns of mammals in three central Western Mediterranean islands from the Late Miocene to Quaternary

An overview of the population histories of three insular realms (Gargano palaeo-archipelago, Sardinia–Maritime Tuscany palaeo-bioprovince and the Sicilian insular complex) during the Late Miocene and Quaternary are here presented. The complexity of biodiversity changes in the islands is analysed to propose an interpretation of origination and extinction patterns. The study highlighted several important aspects of insular faunas. Evolutionary radiations were found to contribute significantly only to the Gargano faunal diversity, likely because the area was an archipelago at the time. Another interesting result is that large and small mammals do not disperse and become extinct all at the same time on each island. In fact, because of their distinct body sizes, large and small mammals have different dispersal ability and therefore different chances to cross-filtering barriers. But distinct body sizes means also different influence on diversity, resistance to environmental changes and likelihood of extinction. Another important point is that large mammalian carnivores at the top of the trophic net are quite more fragile and susceptible to become extinct than other predators. The study finally shows the clear influence that the intense Middle and Late Pleistocene climate-driven environmental changes had on island communities. The reconstruction of the faunal histories of Sardinia and Sicily shows that without exchanges with the mainland the island system represents a rather stable refuge area not too affected by the changes in the “physical” parameters of the environment. In contrast, if the island is frequently connected with the continent, insular faunal assemblages tend to behave as their mainland counterparts.

Linking individuals with ecosystems: experimentally identifying the relevant organizational scale for predicting trophic abundances.

Ecosystems are complex owing to the fact that emergent properties like trophic structure and productivity depend on details related to lower-scale interactions among individuals. A key challenge is identifying how much individual-level detail is needed to predict patterns at the ecosystem level. We tested for the effect of individual herbivore body size on trophic interactions and consequent abundances of plant and herbivore trophic levels in a New England meadow ecosystem. Body size is an important determinant of vulnerability to predation and thus should influence the way individuals tradeoff time spent foraging against time spent avoiding contact with predators. Such tradeoffs can then influence the degree of damage herbivores inflict on their plant resources. We experimentally assigned field-caught grasshoppers to three distinct body size treatment groups (small, normal, and large) and crossed them with two spider predator treatments (spider present and absent) in a fully replicated design. We observed size-dependent differences in grasshopper survival and development. Moreover, predators caused grasshoppers to inflict greater damage to herbs and lesser damage to grasses relative to treatments without predators. However, there were no size-dependent differences in net damage level on grasses and herbs in either predator or no predator treatments owing to size-dependent compensation in grasshopper foraging effort. We thus conclude that in this ecosystem the foraging-predation risk tradeoff displayed by typical or average-sized herbivore is a sufficient amount of individual-level detail needed to explain ecosystem patterns.

Insect species diversity, abundance and body size relationships

BIOLOGICAL diversity, population size and body size are interde-pendent1–8, but there is little consensus on the nature or causes of these relations. Here we analyse the most thoroughly sampled ecological community to date, a grassland insect community sample containing 89,596 individuals of 1,167 species. Each taxonomic order had a distinct body size at which both species richness and number of individuals were highest, but these peak sizes varied more than 100-fold among five major orders. These results suggest that there may be fewer undiscovered small insect species than previously thought. Moreover, we found a sur-prisingly strong, simple, but unreported, relation between species richness (S) and the number of individuals (I) within size classes, S = I0.5. Because this held across numerous body types and a 100,000-fold body-size range, there may be a general rule that is independent of body size for the relations among interspecific resource division, abundance and diversity.

Polyploidy and body size variation in a natural population of the rotifer Euchlanis dilatata

Polyploidy has been reported in many plant species and in some animal species (reviewed by Lewis, 1980 and Suomalainen et al., 1987, respectively). A common consequence of polyploidy in plants is an increase in size (Lewis, 1980; Tal, 1980; Levin, 1983). In animals, most of the studies supporting this generalization are based on comparisons of body sizes of individuals from different populations. In this case, body size variation may reflect environmental differences to which populations of different ploidy are adapted. Very few comparisons of sympatric diploid and polyploid individuals are available either to support or counter this generalization. In Artemia parthenogenetica, pentaploids are larger than sympatric diploids (Wang, 1988). However. in the unisexual fish Poeciliopsis monachu-lucida triploids usually grow more slowly and have a smaller body size than sympatric diploids (Schultz, 1982). In rotifers, interpopulation variation in body size among geographically or temporally separated populations may have a genetic basis (King and Serra, 1980; Yufera, 1982; Serra and Miracle, 1983; She11 and Carrillo, 1984). Morales ( 1987) surveyed lakes in the Sierra Nevada, Spain, and found considerable body size variation in Euchlunis dilatata among the lakes. Morales-Baquero (1988) quantified this variation morphometrically for E. d&tutu from 70 populations. He reported body sizes ranging from 177 pm-340 pm in length and from 125 pm-270 pm in width. He concluded that interlake variation was a more important determinant of body size than intralake factors and hypothesized that these differences might have a genetic basis. The genetic basis underlying body size variation has not previously been investigated in any rotifer. One of us (EJW) noted substantial intrapopulational body size variation in E. dilatata collected from Devils Lake (Lincoln County, Oregon), with animals of two distinct body sizes found during 12 months of intensive sampling. Animals with the

Aedes Triseriatus (Diptera: Culicidae) and La Crosse Virus III. Enhanced Oral Transmission by Nutrition-Deprived Mosquitoes1

Adult Aedes triseriatus , reared as larvae under a dietary regimen that produced 3 distinct body size classes [small (S), normal (N), and large (L)], were orally infected with La Crosse (LAC) virus. In all trials female mosquitoes that had endured the severest nutritional deprivation as larvae (S class) transmitted LAC virus at rates considerably higher than the mosquitoes from the moderately deprived N and nondeprived L classes (mean transmission rates of 82, 54, and 52%, respectively). While the S class mosquitoes ingested a proportionally larger infectious blood meal in relation to dry weight than the other 2 classes, the actual amount of virus ingested varied only about 0.4 log10 plaque-forming units/0.1 mg dry body weight among the 3 size classes. Thus, while enhanced oral transmission may be dose related to some extent, it is also apparent that adult mosquitoes nutritionally deprived as larvae may be physiologically less resistant to infection by LAC virus than less deprived individuals. These results indicate that virus transmission experiments conducted with adult mosquitoes reared on optimal larval diets in the laboratory may not reflect the vector capacity found in field populations. Consequently, epidemiologically important variables such as oral transmission rates may have been seriously underestimated in many previous studies.