Intraspecific Tests Research Articles

Brighter is darker: the Hamilton–Zuk hypothesis revisited in lizards

Abstract Several studies of lizards have made an erroneous interpretation of negative relationships between spectral brightness and parasite load, and thus provided misleading support for the Hamilton–Zuk hypothesis (HZH). The HZH predicts that infected hosts will produce poorer sexual ornamentation than uninfected individuals as a result of energetic trade-offs between immune and signalling functions. To test whether there is a negative relationship between spectral brightness and pigment content in the skin of lizards, we used spectrophotometry to quantify the changes in spectral brightness of colour patches of two species after chemically manipulating the contents of orange, yellow and black pigments in skin samples. Carotenoids were identified using high-performance liquid chromatography. In addition, we compared the spectral brightness in the colour patches of live individuals with differential expression of nuptial coloration. Overall, the analyses demonstrated that the more pigmented the colour patch, the darker the spectrum. We provide a comprehensive interpretation of how variation in pigment content affects the spectral brightness of the colour patches of lizards. Furthermore, we review 18 studies of lizards presenting 24 intraspecific tests of the HZH and show that 14 (58%) of the tests do not support the hypothesis.

A synthesis of local adaptation to climate through reciprocal common gardens

Abstract Contrasts of differences within plant species and ecotypes are often best examined in ecology, evolution and genetics through provenance and biogeographical comparisons. Climate adaptation studies in plants are no exception and benefit from experiments that use these sets of factors. Reciprocal common gardens are a tool used to test for local adaptation in species to different contexts including climate. A synthesis of common gardens and intraspecific tests for climate adaptation was used to compile over 200 studies that explored the relative efficacy of this tool and the ecology of change. Exclusion criteria were applied to review this literature and to compile specific tests that explicitly examined climate, plants and reciprocity in gardens for a total of 70 independent instances. A meta‐analysis was used to test for consistency and significance of detecting ecotypes for the different categories of traits tested and by the transplanting of seeds or seedlings. This meta‐analysis provides clear evidence for plant adaptation to climate change because all significant effect size estimates were positive, relatively large, and both seed and seedling transplants demonstrated consistent evidence for local adaptation. Emergence and germination responses from seed transplant experiments and relative growth and biomass differences from seedling transplants provided particularly strong support. Synthesis. Reciprocal common gardens were a highly effective experimental design to test for ecotypic differentiation and for climate adaptation. Nonetheless, we propose that future studies clearly define whether ecotypes are being explicitly tested in common garden experiments to enable evidence syntheses and discovery, and we highlight the need for reciprocal climatic gardens to clearly test for continued capacity for local adaptation in response to divergent climate selection processes in many plant species.

Can competitive asymmetries maintain offspring size variation? A manipulative field test.

Offspring sizes vary within populations but the reasons are unclear. Game-theoretic models predict that selection will maintain offspring-size variation when large offspring are superior competitors (i.e., competition is asymmetric), but small offspring are superior colonizers. Empirical tests are equivocal, however, and typically rely on interspecific comparisons, whereas explicit intraspecific tests are rare. In a field study, we test whether offspring size affects competitive asymmetries using the sessile marine invertebrate, Bugula neritina. Surprisingly, we show that offspring size determines whether interactions are competitive or facilitative-large neighbors strongly facilitated small offspring, but also strongly competed with large offspring. These findings contradict the assumptions of classic theory-that is, large offspring were not superior competitors. Instead, smaller offspring actually benefit from interactions with large offspring-suggesting that asymmetric facilitation, rather than asymmetric competition, operates in our system. We argue that facilitation of small offspring may be more widespread than currently appreciated, and may maintain variation in offspring size via negative frequency-dependent selection. Offspring size theory has classically viewed offspring interactions through the lens of competition alone, yet our results and those of others suggest that theory should accommodate positive interactions in explorations of offspring-size variation.

Identification and characterization of Choanephora spp. causing Choanephora flower rot on Hibiscus syriacus

Hibiscus syriacus, as a national flower of Korea, is most popularly used for ornamental purposes and includes numerous cultivars, and it is widely planted in temperate zones that feature hot summers. We investigated Choanephora flower rot on H. syriacus from 2012 to 2014 in Korea and Japan and confirmed Choanephora infection in several localities in both countries. Here, our objectives were to identify the main causal agent of Choanephora flower rot on H. syriacus and describe its morphological and molecular characteristics. We identified 44 out of 50 isolates as Choanephora cucurbitarum and the remainder as C. infundibulifera based on morphological characterization and phylogenetic analysis. The sequences of the internal transcribed spacer region (ITS) of ribosomal DNA and the D1/D2 region of the large subunit (LSU) rDNA of examined isolates were compared with sequences obtained from GenBank, and the analysis of the results revealed 100 % identity with the corresponding sequences of C. cucurbitarum and C. infundibulifera strains. Classification of the Choanephora species performed here according to the key described by Kirk (1984) corresponded with the results of the phylogenetic analysis of this study. Through intraspecific and interspecific mating tests, the characteristics of zygospore were described in details. Pathogenicity tests using both species showed the same symptoms, causing blossom blight and soft rot on the flowers, which were identical to those observed in the field. All identified causal agents of Choanephora rot were indeed Choanephora species, where C. cucurbitarum was identified in the majority, while the others were in the minority of examined samples.

Exploring the universal ecological responses to climate change in a univoltine butterfly.

Animals with distinct life stages are often exposed to different temperatures during each stage. Thus, how temperature affects these life stages should be considered for broadly understanding the ecological consequences of climate warming on such species. For example, temperature variation during particular life stages may affect respective change in body size, phenology and geographic range, which have been identified as the "universal" ecological responses to climate change. While each of these responses has been separately documented across a number of species, it is not known whether each response occurs together within a species. The influence of temperature during particular life stages may help explain each of these ecological responses to climate change. Our goal was to determine if monthly temperature variation during particular life stages of a butterfly species can predict respective changes in body size and phenology. We also refer to the literature to assess if temperature variability during the adult stage influences range change over time. Using historical museum collections paired with monthly temperature records, we show that changes in body size and phenology of the univoltine butterfly, Hesperia comma, are partly dependent upon temporal variation in summer temperatures during key stages of their life cycle. June temperatures, which are likely to affect growth rate of the final larval instar, are important for predicting adult body size (for males only; showing a positive relationship with temperature). July temperatures, which are likely to influence the pupal stage, are important for predicting the timing of adult emergence (showing a negative relationship with temperature). Previous studies show that August temperatures, which act on the adult stage, are linked to range change. Our study highlights the importance of considering temperature variation during each life stage over historic time-scales for understanding intraspecific response to climate change. Range edge studies of ectothermic species that have annual life cycles, long time-series occurrence data, and associated temperature records (ideally at monthly resolutions) could be useful model systems for intraspecific tests of the universal ecological responses to climate change and for exploring interactive effects.

The Prevalence and Importance of Competition Among Coral Reef Fishes

Although competition is recognized as a core ecological process, its prevalence and importance in coral reef fish communities have been debated. Here we compile and synthesize the results of 173 experimental tests of competition from 72 publications. We show that evidence for competition is pervasive both within and between species, with 72% of intraspecific tests and 56% of interspecific tests demonstrating a demographically significant consequence of competition (e.g., a decrease in recruitment, survival, growth, or fecundity). We highlight several factors that can interact with the effects of competition and make it more difficult to detect in field experiments. In light of this evidence, we discuss the role of competition in shaping coral reef fish communities and competition's status as one of several processes that contribute to species coexistence. Finally, we consider some of the complex ways that climate change may influence competition, and we provide suggestions for future research.

Genetic diversity does not explain variation in extra-pair paternity in multiple populations of a songbird.

Many songbirds are socially monogamous but genetically polyandrous, mating with individuals outside their pair bonds. Extra-pair paternity (EPP) varies within and across species, but reasons for this variation remain unclear. One possible source of variation is population genetic diversity, which has been shown in interspecific meta-analyses to correlate with EPP but which has limited support from intraspecific tests. Using eight populations of the genetically polyandrous red-winged blackbird (Agelaius phoeniceus), including an island population, we investigated whether population-level differences in genetic diversity led to differences in EPP. We first measured genetic diversity over 10 microsatellite loci and found, as predicted, low genetic diversity in the island population. Additional structure analyses with multilocus genotypes and mtDNA showed the island population to be distinct from the continental populations. However, the island population's EPP rate fell in the middle of the continental populations' distribution, whereas the continental populations themselves showed significant variation in EPP. This result suggests that genetic diversity by itself is not a predictor of EPP rate. We discuss reasons for the departure from previous results, including hypotheses for EPP that do not solely implicate female-driven behaviour.

Biomass explains the intensity of facilitative – not competitive – interactions: three intraspecific tests with annuals

Abstract. Despite efforts to discern the role of plant size in resource competition, the circumstances under which size-dependent plant-plant interactions occur are still unclear. The traditional assumption is that competition intensifies with increasing neighbour size. However, recent studies suggest that the size (biomass) dependence of competitive interactions is strongest at very low biomass levels and becomes negligible after a certain threshold neighbour biomass has been reached. We searched for the generality of such patterns for three common annual plant species in Israel. We monitored target and neighbour biomass along their entire lifecycle using an even-aged, intraspecific and intrapopulation competition screenhouse experiment under water-limited conditions. For all focal species, neighbour presence had a net negative effect on vegetative biomass at harvest. However, this was not explained by increasing neighbour biomass over time, as a consistent pattern of size-dependent facilitative, rather than competitive, interactions was observed at all life stages. We explain these observations in terms of co-occurring aboveground facilitation and dominant belowground competition for water. Since our findings are the first of their kind and contradict theoretical predictions of biomass dependence of net negative interactions, we advocate further experiments addressing size dependence in interactions among plants. In particular, theoretical models addressing size dependence of positive interactions must be developed.

Intra- and interspecific brood recognition in pure and mixed-species honeybee colonies,Apis ceranaandA. mellifera

W e studied the effects of mixed honeybee colonies of Apis mellifera and Apis cerana on the in- traspecific and interspecific recognition of female brood stages in the honeybees A. cerana and A. mellifera by transferring brood combs between queenright colonies. In the intraspecific tests, significantly more lar- vae were removed inA. cerana than in A. mellifera, whilst significantly fewer eggs and pupae were removed in A. cerana than in A. mellifera. In the interspecific tests, A. cerana colonies removed significantly more larvae and pupae of A. mellifera than the same brood stages of A. cerana were removed by A. mellifera. We show there are highly significant differences in both intraspecific and interspecific brood recognition between A. cerana and A. mellifera and that brood recognition operates with decreasing intensity with in- creasing developmental age within species. This suggests that worker policing in egg removal is a first line of defense against heterospecific social parasites.

Latitudinal gradients in species richness in assemblages of sessile animals in rocky intertidal zone: mechanisms determining scale-dependent variability

1. Although latitudinal gradients in species richness within a region are observed in a range of taxa and habitats, little is known about variability in its scale dependence or causal processes. The scale-dependent variability of latitudinal gradients in species richness can be affected by latitudinal differences in (i) the regional relative abundance distribution, and (ii) the degree of aggregated distribution (i.e., intraspecific aggregation and interspecific segregation; henceforth, the degree of aggregation) reflecting differences in ecological processes among regions, which are not mutually exclusive. 2. In rocky intertidal sessile animal assemblages along Japan's Pacific coast (between 31 degrees N and 43 degrees N), scale-dependent variability of the latitudinal gradient in species richness and its causal mechanisms were examined by explicitly incorporating three hierarchical spatial scales into the monitoring design: plots (50 x 100 cm), shores (78 to 235 m), and regions (16.7 to 42.5 km). 3. To evaluate latitudinal differences in the degree of aggregation, the degree of intraspecific aggregation at each spatial scale in each region was examined using the standardized Morishita index. Furthermore, the observed species richness was compared with the species richness expected by random sampling from the regional species pool using randomization tests. 4. Latitudinal gradients in species richness were observed at all spatial scales, but the gradients became steadily more moderate with decreasing spatial scale. The slope of the relative abundance distribution decreased with decreasing latitude. 5. Tests of an index of intraspecific aggregation and randomization tests indicated that although species richness at smaller scales differed significantly from species richness expected based on a random distribution, the degree of aggregation did not vary with latitude. Although some ecological processes (possibly species sorting) may have played a role in determining species richness at small spatial scales, the importance of these processes did not vary with latitude. 6. Thus, scale-dependent variability in the latitudinal gradient of species richness appears to be explained mainly by latitudinal differences in the regional relative abundance distribution by imposing statistical constraint caused by decreasing grain size.

Extrapair paternity, migration, and breeding synchrony in birds

To understand interspecific patterns in the strength of sexual selection, variation in the costs and benefits of exercising mate choice needs to be evaluated. One manifestation of sexual selection in birds is the occurrence of greatly variable levels of extrapair paternity (EPP). A proposed general explanation for this variation is that the benefits to females in seeking extrapair copulations vary in a predictable manner according to the degree of breeding synchrony because females are better able to assess potential extrapair partners when males are simultaneously in breeding condition. This hypothesis predicts a latitudinal trend in EPP because birds tend to breed more synchronously away from the equator. Expanding on previous geographically and taxonomically restricted tropical/temperate comparisons, we used phylogenetically independent standardized linear contrasts to show that this positive relationship persists when all bird species for which EPP estimates currently exist are considered. However, if a third factor covaries with latitude in the same way as breeding synchrony and EPP, this relationship need not be causal. Migration could also account for latitudinal variation in the benefits to females of pursuing EPP, if migration is associated with (1) hasty or (2) inaccurate mate choice, (3) facilitated assessment of male quality through the condition-dependence of arrival time, or (4) increased genetic variance in male quality. We show that migration distance is positively related to the proportion of EPP and that migration can statistically explain the latitudinal trend in EPP, even when confounding factors are simultaneously controlled. Hence, alternative explanations for latitudinal variation in EPP may be feasible, and careful intraspecific tests are needed to assess their relative importance and their implications for geographical variation in life-history evolution. Key words: breeding synchrony, comparative analysis, extrapair paternity, migration, sexual selection. [Behav Ecol 15:41–57 (2004)]

Intracolonial patterns of reproduction in the queen-size dimorphic ant Leptothorax rugatulus

Animals that live in genetically heterogeneous groups are faced with a combination of cooperation and conflict. Reproductive skew theory aims to provide a unified theory of the partitioning of reproduction in animal societies by combining genetic, demographic, and environmental factors. Although theoretical elaborations abound, empirical data are rare. Specifically, explicit intraspecific tests are scarce and have provided conflicting results. We present data on reproductive partitioning among queens in the ant Leptothorax rugatulus with special emphasis on relatedness and body size. Relatedness was negatively correlated to skew in sexual offspring and uncorrelated to skew in total offspring. Body size was not correlated to a queen's reproductive share. Thus, we did not find any support for the classic optimal skew models that are based on concessions. In artificial colonies, composed of randomly selected, unrelated workers and queens, reproductive skew was higher than in natural colonies, which suggested that unequal reproduction among queens could arise without nepotism by workers. Again, a queen's body size was not a good indicator of her reproductive share, but egg laying rate was. In colonies that contained large and small queens, small queens produced proportionally more sexual offspring. Although this result is in accordance with the kin conflict over caste determination hypothesis, it is more plausibly explained by an adaptation of the caste ratios to alternative dispersal tactics.

Ultimate Causation of Aggressive and Forced Copulation in Birds: Female Resistance, the CODE Hypothesis, and Social Monogamy

SYNOPSIS. Except in ducks and geese (Anseriforms), aggressive or forced copulation in birds is rare. The rarity of forced copulation in birds theoretically is due to morphological and physiological mechanisms of female resistance that place fertilization most often under female control. Traits theoretically associated with resistance by females include: digestive epithelium lining the section of the cloaca receiving sperm and powerful doacal musculature used to eject contents, including waste material and sperm. These traits suggest that the Immediate Fertilization Enhancement Hypothesis may be an inadequate ultimate explanation for forced copulation when it occurs. Ideas in Heinroth (1911) and Brownmiller (1975) suggested an alternative, the CODE Hypothesis, which says that aggressive copulation creates a dangerous environment for females. This, in turn, fosters male mating advantage via social monogamy, because selection sometimes favors females who trade sexual and social access for protection from male aggression. Thus, theoretically, trades of protection for copulation favor the evolution of social monogamy even in species with little or no paternal care. Individual males may accrue selective advantages through direct benefits, kin-selected benefits, or reciprocal altruism. The CODE hypothesis for social monogamy predicts variation in extrapair paternity from preferred mates, variation in male reproductive success, and variation among females' post-insemination resistance mechanisms as functions of variation among females' vulnerabilities (ecological and intrinsic) to aggressive copulation. Observers will base intraspecific tests on variation among females in their vulnerabilities to male aggression against them.

The Hamilton and Zuk Hypothesis Revisited: a Meta-Analytical Approach

Abstract The Hamilton & Zuk (1982) hypothesis of parasite-mediated sexual selection has been the subject of both inter- and intraspecific tests. Past reviews have used vote counting to determine whether this hypothesis is supported by empirical evidence. This study reanalysed 199 separate quantitative assessments of a central prediction of the Hamilton & Zuk hypothesis using meta-analytical techniques. Overall, our meta-analysis showed that there was a significant negative effect of parasites on male showiness as predicted. However the magnitude of this effect varied between host taxa and between endo and ectoparasitic taxa. As a whole intraspecific correlations between parasite load and male showiness provided very little support for the hypothesis with only the effect of parasites on fish morphology matching the Hamilton & Zuk prediction. There was more support for the hypothesis from interspecific studies especially those based upon the original Hamilton & Zuk (1982) data set, although other bird studies provided weaker support. The generality of the Hamilton & Zuk hypothesis in respect to parasite mediated sexual selection across taxa is thrown into doubt by these results. However, in some specific host-parasite systems the role of parasites appears important and future intraspecific tests of parasite-mediated sexual selection should perhaps focus on such systems.

Intraspecific Variation in Plumage Coloration Reflects Immune Response in Great Tit (Parus major) Males

1. The Hamilton and Zuk hypothesis proposes that within species, individuals with more elaborate secondary sexual traits signal their higher resistance to parasites. 2. Intraspecific tests of the correlation between secondary sexual traits and parasite load have given equivocal results, probably because of difficulties in deciding which parasite species are important for the process of sexual selection. 3. In this study we use a different approach by relating secondary sexual traits to the level of immune response in the hosts rather than the parasite load. It is well known that the number and proportions of different types of leucocytes reflect the health status of individuals, as these cells quickly respond to stress and infectious diseases. 4. The number and proportions of different types of leucocytes were counted in blood smears from male Great Tits, Parus major, and the intensities of the males' yellow plumage coloration were scored, in 1991 and 1992 on Gotland, SE Sweden. 5. We found a positive correlation between number and proportion of heterophils and colour intensity. 6. More than one interpretation is possible though we favour the view that brighter males signal low parasitation intensity as a result of their superior immunity.

Pasture soils as carbon sink

Pasture soils as carbon sink

Hunting Social Wasp Interactions: Influence of Prey Size, Arrival Order, and Wasp Species

To determine the effects of wasp species, nest affiliation, arrival order, and prey size on choice of and access to prey and on agonistic behavior among hunting wasps, I observed interactions among Polybia occidentalis and Polybia diguetana (Hymenoptera: Vespidae) prey foragers in Guanacaste, Costa Rica. Wasps were trained to forage on Bagisara repanda (Lepidoptera: Noctuidae) larvae at a test site, and trained wasps were used in experiments. The presence of another forager influenced the choice of an access to prey by hunting wasps. In choice tests, both species preferentially hovered near prey occupied by another Polybia forager rather than unoccupied 0.5—cm pieces of prey, but their subsequent responses differed. Polybia occidentalis foragers tended to land with other Polybia foragers of either species and to gain access to the occupied prey. Polybia diguetana foragers did not land preferentially with other Polybia. In intra— and interspecific tests of wasp pairs, tolerance among wasps varied with prey size. The greatest percentage of highly agonistic activity occurred when the resident was on the largest piece of prey that she had a chance of being able to carry away. As the size of prey increased above that, the percentage of highly agonistic behavior decreased. In intraspecific tests, P. occidentalis foragers did not treat nestmates preferentially. In cross—species tests, both prey availability and the arrival order of wasps affected the tolerance of wasps. There was a lower overall percentage of agonistic behavior in tests where the slightly larger wasp, P. occidentalis, arrived first. Hunting Polybia foragers behaved as if using the following rules: (1) If a forager was able to fly off with prey and avoid conflict, she picked up the prey and fled. (2) She fought if she had a chance of excluding others and monopolizing the prey. (3) If the prey was large, the two foragers split it. Both the defensibility of the prey and the ability of the wasps to take advantage of this defensibility structured the interactions among hunting wasps. These interactions influenced the hunting success of wasps and are therefore determinants of nest productivity. Interactions among foragers thus may bear on the diversity and abundance of social wasps.

THE EXPERIMENTAL ASSESSMENT OF FITNESS IN DROSOPHILA. I. COMPARATIVE MEASURES OF COMPETITIVE REPRODUCTIVE SUCCESS

Strains of D. melanogaster, representing a range of genetic diversity, were systematically subjected to each of several techniques that have been devised to assess total or net fitness. All of these techniques operationally define fitness in terms of reproductive success under competitive conditions. For the set of strains tested, an excellent correlation was obtained between the competitive indices produced by two single-generation intraspecific competitions, despite fundamental differences in the strains used as competitive standards. The results of two interspecific tests were also correlated, but the intraspecific vs. interspecific test result comparisons ranged from highly significant to nonsignificant correlations. For the fitness estimates, the overall variances produced by the intraspecific tests were greater than those obtained in the interspecific competitions. No significant correlations were found between the results of a long-term (multi-generation) competitive assessment of fitness and any of the single-generation tests. Therefore, although all of these tests refer to a net parameter called "fitness", they are clearly not all measuring the same thing. Differences in the competitive interactions operative in each technique are suggested to account for these results.

Incremental changes in deer mouse ( Peromyscus maniculatus) core temperatures during behavioral challenges

1. 1. Second generation deer mice bearing temperature-sensitive radiosondes respond by increasing body temperatures incrementally as a result of exposure to novel environments, visual, physical and contact, with opponents during intra-specific tests of aggression. 2. 2. Physical contact with an opponent results in additional increase in core temperature if the opponent is either of nearly equal or lower social rank. 3. 3. Physical contact with a more aggressive opponent does not result in an increase in core temperature over that recorded during visual contact, but is associated with a drop in core temperature of the submissive animal.

Variation in Rana Pipiens Schreber in Texas

Leopard frogs (Rana pipiens Schreber) from Texas were examined morphologically and used in intraspecific hybridization tests to describe the variation of this anuran in the state. The morphological analysis suggests that there are three morpho-units separated by lines running along the western boundary of the Texan province and the southern boundary of the Kansan province. Hybridization tests indicate that Central x East Texas hybrid embryos are recognizable from their controls only when reared under conditions of salinity stress. This work was initiated to determine whether the leopard frog (Rana pipiens Schreber) has developed a demonstrable morphophysiological gradation of characters along a habitat gradient which extends from Central through East Texas. Specimens from outside the study area were also examined to elucidate statewide trends in morphological variation. This study is based on the examination of 625 adult (i.e., over 45 mm snout-vent length) and 215 juvenile leopard frogs, and upon the results of 76 artificial hybridization experiments. The study was undertaken for several reasons. First, cursory unpublished experiments conducted at the University of Texas had indicated that offspring from crosses between Central and East Texas leopard frogs were not as viable as their controls. Second, the morphology of the adults varies over the state, but this variation has never been adequately described using a large sample of specimens. Third, although numerous crossings experiments with Texas R. pipiens have been conducted (Moore, 1946; 1949), the specimens used have all been collected in Ward County. Genetic variation within the state of Texas as revealed by crossing experiments is therefore an untouched field. Finally, although Moore and others (Moore, 1939, et. seq.; Porter, 1941; Ruibal, 1955, 1957; Volpe, 1957) have attempted to establish the major trends in variation of certain physiological characters of R. pipiens embryos, no one has made a concentrated study of specimens from a relatively small geographic area. I am indebted to Dr. W. F. Blair for suggesting this problem and for advice during its progress. My wife, Martha Kay, assisted in the field collecting and in preparation of the figures.