Competition Trials Research Articles

Sperm competition and offspring viability at hybridization in Australian tree frogs, Litoria peronii and L. tyleri

Hybridization between closely related species often leads to reduced viability or fertility of offspring. Complete failure of hybrid offspring (post-zygotic hybrid incompatibilities) may have an important role in maintaining the integrity of reproductive barriers between closely related species. We show elsewhere that in Peron's tree frog, Litoria peronii, males more closely related to a female sire more offspring in sperm competition with a less related rival male. Observations of rare 'phenotypic intermediate' males between L. peronii and the closely related L. tyleri made us suggest that these relatedness effects on siring success may be because of selection arising from risks of costly hybridization between the two species. Here, we test this hypothesis in an extensive sperm competition experiment, which shows that there is no effect of species identity on probability of fertilization in sperm competition trials controlling for sperm concentration and sperm viability. Instead, there was a close agreement between a male's siring success in isolation with a female and his siring success with the same female in competition with a rival male regardless of species identity. Offspring viability and survival, however, were strongly influenced by species identity. Over a 14-day period, hybrid offspring suffered increasing mortality and developed more malformations and an obvious inability to swim and right themselves, leading to compromised probability of survival. Thus, hybridization in these sympatric tree frogs does not compromise fertilization but has a strong impact on offspring viability and opportunity for reinforcement selection on mate choice for conspecific partners.

Reliability of temperament tests on finishing pigs in group-housing and comparison to social tests

If variation in behaviour is consistent within individuals and reliably associated with relevant welfare measures, this variation could aid in genetic selection, or development of management schemes designed to improve welfare. In this study, we focused on temperament tests in group-housed finishing pigs, with the objective of validating measures that are readily applicable in commercial settings and potentially related to individual differences in stress response. A total of 118 pigs in two replicate studies were housed in pens of 7–8 pigs per pen. At 24 weeks of age, animals were subjected to three tests of fear in the home pen: the human approach test (HAT), novel object test (NOT) and open door test (ODT). In each test, pigs were scored on their latency to contact the human or object, or to leave the home pen. Tests were repeated on three occasions at intervals of 3–4 days. On each test day the HAT was performed twice to compare results between different handlers. Behaviour in tests of fear was compared with two social tests in a subset of 58 pigs. Lesion scoring was performed after mixing as a measure of aggression, and a feed competition test was used to assess social status. Repeatability within-test was evaluated in a mixed model with pig as a random effect, and agreement between days, handlers and tests was evaluated by partial correlations after controlling for replicate, pen and day effects. Latency to perform all three fear tests decreased significantly over time. Correlations within-test showed significant agreement between all days for HAT and ODT, and between HAT handlers. Between tests, the HAT and ODT were correlated, and ODT and NOT tended to correlate. Comparisons between group fear tests and social tests showed that pigs which readily approach a human tended to have higher lesion scores and fewer feeding bouts in the feed competition trial. While test latencies decrease with repetition, the HAT and ODT show individual consistency over time, which suggests that these tests describe behavioural tendencies and may be useful for predicting fearful responses at slaughter.

Southern pollen sired more seeds than northern pollen in southern seed orchards established with northern clones of Pinus sylvestris

Contamination by southern pollen is a considerable problem in Scots pine (Pinus sylvestris L.) seed orchards established with northern clones. This study investigated whether the contamination was due to the competitive superiority of southern pollen by carrying out competition trials using mixtures of pollen from northern and southern populations of Scots pine. Trials were performed in a southerly seed orchard established with clones originating from northern populations. Seed paternity (siring) was determined through the analysis of allozyme variation. Southern genotypes sired significantly more seeds (76%) than their northern competitors and across all mixed-pollen crosses. Maternal genotype had no effect on seed siring success. The mean flower abortion rate was lower in southern pure-pollen crosses and mixed-pollen crosses than in northern pure-pollen crosses. The results show that local pollen may induce high levels of background pollination in southern seed orchards composed of northern genotype grafts. These results must be taken into account when aiming to produce suitable reforestation material for northern areas.

Medidas do grau de precisão experimental em ensaios de competição de cultivares de milho

O objetivo deste trabalho foi avaliar a adequação de algumas estatísticas como medidas do grau de precisão experimental, e as relações entre elas. Foram usados os dados de produtividade de grãos de 101 ensaios de competição de cultivares de milho (Zea mays L.), realizados no Estado do Rio Grande do Sul, nos anos agrícolas 2002/2003, 2003/2004 e 2004/2005. Foi estudada a relação entre 12 estatísticas, estimadas para cada ensaio, e as análises de correlação de trilha e de agrupamento foram realizadas com base nessas estatísticas. Os limites de classe estabelecidos, a partir das estatísticas acurácia seletiva, herdabilidade, coeficiente de determinação e valor do teste F para cultivar, mostraram-se adequados para estimar o grau de precisão experimental de ensaios de competição de cultivares de milho. Por essas estatísticas, 89% dos ensaios de competição de cultivares de milho apresentaram precisão alta ou muito alta e 5% dos ensaios poderiam ser escartados em razão da insuficiência na precisão experimental. As estatísticas acurácia seletiva, herdabilidade, coeficiente de determinação e valor do teste F para cultivar têm relação direta entre si e são mais adequadas do que o coeficiente de variação e a diferença mínima significativa pelo teste de Tukey, em percentagem da média, para avaliação da precisão experimental em ensaios de competição de cultivares de milho.

Teores de óleo, proteínas e produtividade de soja em função da antecipação da semeadura na região oeste do Paraná

A semeadura antecipada da soja, particularmente utilizando cultivares precoces, é prática que vem sendo adotada por muitos produtores paranaenses com o intuito de antecipar a colheita e viabilizar o cultivo de milho safrinha. Visando avaliar a influência da antecipação da semeadura na composição química e na produtividade da soja, foram instalados ensaios de competição de cultivares na unidade da COODETEC, em Palotina (PR). O delineamento foi em blocos casualizados, desenvolvido em dois anos agrícola (2003/2004 e 2004/2005), com três cultivares precoces (CD 202, CD 215 e CD 216), semeadas em cinco épocas (15/9, 30/9, 15/10, 30/10 e 15/11). Foram determinados os teores de óleo e proteínas nos grãos. Partindo-se do rendimento de grãos nas parcelas, foram calculadas as produtividades em kg ha-1. Os dados coletados foram submetidos à análise de variância conjunta e realizados os desdobramentos das interações quando necessários. Os resultados permitiram concluir que a antecipação da semeadura influenciou na produtividade e composição química dos grãos.

QUALIDADE FISIOLÓGICA E SANITÁRIA DAS SEMENTES SOB SEMEADURA ANTECIPADA DA SOJA

A semeadura antecipada da soja, particularmente com cultivares precoces, é prática que vem sendo adotada por muitos produtores paranaenses com o intuito de antecipar a colheita da cultura e viabilizar o cultivo de milho safrinha. Com o objetivo de avaliar a influência da antecipação da semeadura na qualidade fisiológica e sanitária das sementes de soja, foram instalados ensaios de competição de cultivares na unidade da COODETEC, em Palotina, PR. O delineamento foi em blocos casualizados, conduzido em duas safras (2003/2004 e 2004/2005), com três cultivares precoces (CD 202, CD 215 e CD 216), semeadas em cinco épocas (15/09, 30/09, 15/10, 30/10 e 15/11). A qualidade fisiológica das sementes de soja foi avaliada por meio dos testes de germinação (primeira contagem e contagem final) e de tetrazólio (vigor e viabilidade). O “blotter test” foi aplicado para caracterizar a sanidade das sementes. Os dados coletados foram submetidos à análise de variância conjunta e realizados os desdobramentos das interações quando necessários. Os resultados obtidos indicaram que a semeadura em 30/10 foi favorável à obtenção de sementes com melhor qualidade.

Sperm competition and fertilization success of Atlantic halibut ( Hippoglossus hippoglossus L.)

Sperm competition trials were conducted to study the fertilization ability of sperm from four Atlantic halibut ( Hippoglossus hippoglossus L.) males. Sperm from four males were mixed using equal number or equal volume of sperm from each of the males to fertilize eggs from two females. The proportions of larvae sired by the different males were quantified using DNA microsatellite analyzes. Larvae sired by Male 2 dominated the offspring in the trials; this male sired 79% and 78% of the DNA-analyzed offspring of two females. Reducing the number of sperm cells to below 10 5 did not significantly alter the relative proportion of offspring sired by the different males. Male 2 provided 25 and 27% of the total sperm in experiments with equal volumes and equal numbers of sperm, respectively. However, Male 2 provided 47% to 50% of the motile spermatozoa in the mixtures. Furthermore, Male 2 also had the highest sperm velocity (115.7 µm/s). Motility-related sperm traits may partly explain why offspring from Male 2 dominated the larvae. In both control and experimental groups, fertilization rates were high (> 90%) when sufficient numbers (10 5–10 6) of spermatozoa per egg were used, and the fertilization success did not depend on whether sperm from one, or from a mixture of four males were used. Uncritical use of pooled sperm from different males during fertilization may cause unexpected results with only a few parents represented in an offspring population. Mixing sperm from different males without exact knowledge of sperm motility parameters may ultimately lead to low genetic variability, inbreeding, and strains with low fitness.

Factors predicting male fertilization success in an external fertilizer

In postcopulatory sexual selection both sperm competition and cryptic female choice are considered to be important selective agents, but their relative importance for male fertilization success has received little attention. We tested whether sperm quality, male spawning coloration, male heterozygosity, and genetic overlap with the female explained a male’s fertilization success in controlled in vitro fertilization competition trials between equal numbers of sperm from pairs of male Arctic charr (Salvelinus alpinus), an external fertilizer. Offspring were genotyped to determine each males’ share of paternity. The velocity of a male’s sperm relative to the velocity of the competing male’s sperm was the best predictor of male fertilization success. Yet, sperm velocity was not related to spawning coloration or male heterozygosity. In fact, the most brightly colored male in a pair had the lowest fertilization probability. This could result from cryptic female choice for pale males, but might rather be a result of paler males producing more competitive sperm than more colored males. Furthermore, the more microsatellite alleles a male shared with the female relative to the competing male, the higher fertilization success he had. We argue that this latter may be an effect of assortative cryptic female choice, which might prevent hybridization with sympatric Arctic charr morphs or one form of kin selection.

Males with high genetic similarity to females sire more offspring in sperm competition in Peron's tree frogLitoria peronii

Recent work has confirmed that genetic compatibility among mates can be an important determinant of siring success in sperm competition experiments and in free-ranging populations. Most of this work points towards mate choice of less related mates. However, there may also be the potential for mate choice for intermediate or even genetically similar mates to prevent outbreeding depression or hybridization with closely related taxa. We studied relatedness effects on post-copulatory gametic choice and/or sperm competition in an external fertilizer, Peron's tree frog (Litoria peronii), since external fertilizers offer exceptional control in order to test gametic interaction effects on probability of paternity and zygote viability. Sperm competition experiments were done blindly with respect to genetic relatedness among males and females. Thereafter, paternity of offspring was assigned using eight microsatellite loci. Three hybridization trials between L. peronii and a closely related sympatric species Litoria tyleri were also carried out. In the sperm competition trials, males that are more genetically similar to the female achieved higher siring success compared with less genetically similar males. The hybridization trials confirmed that the two species can interbreed and we suggest that the risk of hybridization may contribute to selection benefits for genetically more similar males at fertilization. To our knowledge, this study is the first to show evidence for post-copulatory selection of sperm from genetically more similar individuals within a natural population.

Mating system variation and morph fluctuations in a polymorphic lizard

In polymorphic male painted dragon lizards (Ctenophorus pictus), red males win staged contests for females over yellow males, and yellow males have greater success in staged sperm competition trials than red males. This predicts different reproductive strategies in the wild with red males being more coercive or better mate guarders than yellow males. Yellow males would be expected to sire more offspring per copulation and have a greater proportion of offspring from clutches with mixed paternity. However, here we show using microsatellites that the frequency of mixed paternity in the wild is low (< 20% on average across years), that all morphs on average have the same number of offspring sired per year, and that mating system variation (polyandry vs. monandry) is strongly correlated with perch density on male territories. Furthermore, a logistic regression on male successful vs. unsuccessful mate acquisition showed that red males were under negative selection when they dominated the population, which suggests ongoing frequency dependent selection on male colouration.

Concurrent niche and neutral processes in the competition–colonization model of species coexistence

The importance of neutral dynamics is contentiously debated in the ecological literature. This debate focuses on neutral theory's assumption of fitness equivalency among individuals, which conflicts with stabilizing fitness that promotes coexistence through niche differentiation. I take advantage of competition-colonization trade-offs between species of aquatic micro-organisms (protozoans and rotifers) to show that equalizing and stabilizing mechanisms can operate simultaneously. Competition trials between species with similar colonization abilities were less likely to result in competitive exclusion than for species further apart. While the stabilizing mechanism (colonization differences) facilitates coexistence at large spatial scales, species with similar colonization abilities also exhibited local coexistence probably due to fitness similarities allowing weak stabilizing mechanisms to operate. These results suggest that neutral- and niche-based mechanisms of coexistence can simultaneously operate at differing temporal and spatial scales, and such a spatially explicit view of coexistence may be one way to reconcile niche and neutral dynamics.

Effects of sodium valproate and carbamazepine on food competition aggression in pigeons

Valproate and carbamazepine (CAR) have been proposed as adjunct alternatives for the control of aggression in psychiatric patients, although no definite conclusions have been reached. We examined the effects of these drugs on food competition offensive aggression and other behaviors in high- and low-aggression food-restricted pigeons. These were divided into pairs containing previously ranked high-aggression (N = 10 pairs) and low-aggression females (N = 10 pairs). In Experiment 1, a pigeon in each pair of high- and low-aggression subjects was treated daily with an oral dose of sodium valproate (50 mg kg-1 mL saline-1) for 15 days. The other animal received the vehicle. On days 1, 7, and 15, food competition trials (10 min) were performed 60 min after treatment. In Experiment 2, one pigeon in each pair was treated daily with an oral dose of CAR (20 mg kg-1 mL saline-1) for 15 days. Each pair was submitted to a food competition trial on days 1, 7, and 15 of treatment. Valproate (15 days of treatment) selectively decreased the time spent in offensive aggression (control: 102.7 +/- 9.3 vs valproate: 32.7 +/- 9.2 s; P < 0.001, ANOVA-2-TAU) of high-aggression pigeons. This was also the case for 7 and 15 days of CAR treatment (control: 131.5 +/- 8.9 vs CAR: 60.4 +/- 5.3, P < 0.01, and control: 122.7 +/- 7.1 vs CAR: 39.1 +/- 5.2; P < 0.001, ANOVA-2-TAU, respectively). Thus, the two anticonvulsive drugs have a similar effect on food competition aggression in pigeons.

SHORTER SPERM CONFER HIGHER COMPETITIVE FERTILIZATION SUCCESS

Spermatozoa exhibit taxonomically widespread patterns of divergent morphological evolution. However, the adaptive significance of variation in sperm morphology remains unclear. In this study we examine the role of natural variation in sperm length on fertilization success in the dung beetle Onthophagus taurus. We conducted sperm competition trials between males that differed in the length of their sperm and determined the paternity of resulting offspring using amplified fragment length polymorphism (AFLP) markers. We also quantified variation in the size and shape of the female's sperm storage organ to determine whether female morphology influenced the competitiveness of different sperm morphologies. We found that fertilization success was biased toward males with relatively shorter sperm, but that selection on sperm length was dependent on female tract morphology; selection was directional for reduced sperm length across most of the spermathecal size range, but stabilizing in females with the smallest spermathecae. Our data provide empirical support for the theory that sperm competition should favor the evolution of numerous tiny sperm. Moreover, because sperm length is both heritable and genetically correlated with condition, our results are consistent with a process by which females can accrue genetic benefits for their offspring from the incitement of sperm competition and/or cryptic female choice, as proposed by the "sexy sperm" and "good sperm" models for the evolution of polyandry.

The role of body size in competition and mate choice in an agamid with female-biased size dimorphism

Competition and mate choice are fundamentally important components of social systems. We investigated intra-sexual competition and inter-sexual competition (mate choice) in Rankinia diemensis, an agamid lizard with female-biased size dimorphism. We examined intra-sexual interactions during contests and mate choice in relation to body size for both males and females. In male-male competition trials, proportions of two display types differed depending on body size, with more tail flicks produced by bigger males, and more hand-waves displayed by smaller males. These behaviours hold particular biological significance for agamid lizards; tail-flicks convey aggressiveness and, therefore, dominance, while hand-waves often denote submissiveness. In female-female competition trials, a greater difference in body size between the two conspecifics resulted in the larger female directing more pushes towards the smaller female. This female competition may be important in the social system and could be involved in resource defence. We found no indication of size-based mate choice for males or females. This suggests mate preferences may not be based on body size in this species. This may be linked to female-biased size dimorphism in this species, but it also supports previous studies that have failed to demonstrate female choice in reptiles.

Estatísticas de avaliação da precisão experimental em ensaios de cultivares de milho

Foram usados dados de produtividade de grãos, de 101 ensaios de competição de cultivares de milho (Zea mays L.), realizados no Estado do Rio Grande do Sul, nos anos agrícolas 2002/2003, 2003/2004 e 2004/2005, com o objetivo de avaliar estatísticas para a classificação da precisão experimental. O coeficiente de variação e a diferença mínima significativa, entre as cultivares pelo teste de Tukey expresso em porcentagem da média, estão associadas à média e à variância residual e são estatísticas adequadas para a classificação de experimentos com médias semelhantes. Os maiores valores das estatísticas herdabilidade, coeficiente de determinação, valor do teste F para cultivar, e o índice de diferenciação de Fasoulas estão associados a maiores variabilidades genéticas e menores variâncias residuais, e independem da média do ensaio; estas estatísticas são adequadas para a classificação da precisão de experimentos.

Boldness is influenced by social context in threespine sticklebacks (Gasterosteus aculeatus)

Summary Boldness refers to the extent to which animals balance risk against benefits when engaging in such behaviors as foraging, exploration or resource competition. Evidence suggests that individuals can behave strategically, acting boldly in situations when doing so is adaptive, whilst avoiding risk when the rewards are correspondingly lower. In this study we sought to determine the effects of social context upon the boldness of threespine sticklebacks (Gasterosteus aculeatus). We found that when individuals were tested alone, those that were more active were more likely to resume foraging sooner when subjected to a simulated predator attack in a separate test, and also consumed more prey in foraging competition trials. We found no effect of group size upon the relative ability of individuals to effectively compete for prey. Group size did affect other behaviours however: focal fish were more active and resumed foraging more rapidly when tested in groups that they did when tested alone. Finally, individual social information use was not correlated with behaviour in other contexts. Two competing hypotheses, the adaptation and the constraint hypotheses have been posited to explain the presence and prevalence of individual variation in boldness; our findings offer partial support for the former of these.

Adequação de ciclo e estatura de planta é essencial para a comparação de genótipos de milho

A falta da comparabilidade dos efeitos nos ensaios de competição de genótipos de milho (Zea mays) pode resultar em recomendações equivocadas. O objetivo deste trabalho foi verificar se o enquadramento dos genótipos de milho quanto ao ciclo é correto e se este altera a comparação das médias. Foram conduzidos seis experimentos de competição de genótipos de milho de ciclo superprecoce, precoce e normal, em dois níveis tecnológicos, na área experimental da UFSM, durante o ano agrícola de 2000/2001. O experimento bifatorial (genótipos nas parcelas principais e densidades nas subparcelas) foi conduzido no delineamento blocos ao acaso com três repetições. A proporção de experimentos de pressuposições adequadas foi alta, indicando análise de boa qualidade. Os genótipos de milho encontram-se mal agrupados quanto ao ciclo e, por conseqüência, quanto à estatura de plantas, aumentando a heterogeneidade nos experimentos e prejudicando a comparação das médias. Genótipos de milho com ciclo e/ou estatura de plantas diferentes não devem ser comparados na mesma densidade e experimento.

Sperm Viability Matters in Insect Sperm Competition

Experimental studies in insects have shown how sperm competition can be a potent selective force acting on an array of male reproductive traits . However, the role of sperm quality in determining paternity in insects has been neglected, despite the fact that sperm quality has been shown to influence the outcome of sperm competition in vertebrates . A recent comparative analysis found that males of polyandrous insect species show a higher proportion of live sperm in their stores . Here, we test the hypothesis that sperm viability influences paternity at the within-species level. We use the cricket Teleogryllus oceanicus to conduct sperm competition trials involving prescreened males that differ in the viability of their sperm. We find that paternity success is determined by the proportion of live sperm in a male's ejaculate. Furthermore, we were able to predict the paternity patterns observed on the basis of the males' relative representation of viable sperm in the female's sperm-storage organ. Our findings provide the first experimental evidence for the theory that sperm competition selects for higher sperm quality in insects. Between-male variation in sperm quality needs to be considered in theoretical and experimental studies of insect sperm competition.

Métodos de correção da produtividade de grãos de milho relacionados à adaptabilidade e estabilidade de cultivares

O objetivo deste trabalho foi verificar a interferência de métodos de correção da produtividade de grãos de milho nos parâmetros adaptabilidade e estabilidade de cultivares. A correção da produtividade de grãos foi avaliada em 31 ensaios de competição de cultivares de milho, por meio dos seguintes métodos: sem correção, regra de três, método de Zuber, covariância da população média, covariância da população ideal, método proposto por Cruz, método proposto por Vencovsky &amp; Cruz e método de correção estratificada. As estatísticas, desvio quadrático médio para cada um dos parâmetros de adaptabilidade e estabilidade e índice de concordância, foram utilizadas para verificar a magnitude da influência das correções. Os métodos covariância para a população média, covariância para a população ideal, Vencovsky &amp; Cruz e correção estratificada são os que acarretam menores discordâncias dos parâmetros de adaptabilidade e estabilidade de cultivares em relação aos dados sem correção.

A precisão experimental relacionada ao uso de bordaduras nas extremidades das fileiras em ensaios de milho

Foram conduzidos quatro experimentos de competição de cultivares de milho, durante o ano agrícola de 2000/2001, e três no ano 2001/2002, na área experimental do Departamento de Fitotecnia da UFSM, Santa Maria, com o objetivo de verificar se o uso de bordadura nas extremidades das fileiras melhora a precisão experimental. Foi usado o delineamento em blocos ao acaso com três repetições, sendo os blocos espaçados entre si de um metro, e as parcelas constituídas por duas fileiras espaçadas de 0,8m com 5,0m de comprimento, com a área útil formada pelos quatro metros centrais. Para a variável rendimento de grãos de milho, procedeu-se a verificação das pressuposições do modelo, a análise da variância com teste F e a aplicação do teste Scott-Knott para as comparações entre as médias estimadas na área útil e na área total. A estatística diferença mínima significativa pelo teste de Tukey foi usada como principal indicador da precisão, cuja significância foi testada pelo teste F dos respectivos quadrados médios do erro. Todas as pressuposições do modelo matemático, nos sete experimentos, foram atendidas. Para o rendimento de grãos, o descarte dos resultados da bordadura nas extremidades das fileiras não altera a precisão experimental na comparação de cultivares.