Sexual dimorphism in the earwig Labidura xanthopus (Dermaptera): a macroecological approach to patterns and process

O dimorfismo sexual varia consideravelmente entre populações dentro de uma mesma espécie. Essa variação na direção e na magnitude do dimorfismo sexual é, em parte, devida às diferenças sexuais na respostas plásticas às condições e aos recursos ambientais. Por meio de experimentos em laboratório, sabe-se que a temperatura e a disponibilidade de alimento são fatores importantes na geração de variações morfológicas inter-individuais e que seus efeitos diferem entre machos e fêmeas. Usamos indivíduos da tesourinha Labidura xanthopus (Dermaptera) coletados em 20 localidades ao longo da costa brasileira para investigar como o tamanho corporal e o tamanho do armamento de machos e fêmeas variam em um gradiente natural de temperatura. O tamanho do corpo diminuiu com o aumento da temperatura, mas o dimorfismo sexual se manteve constante ao longo do gradiente de temperatura. Para o tamanho do armamento, encontramos uma relação negativa para machos e positiva para fêmeas. Conseqüentemente, a magnitude do dimorfismo sexual no tamanho do armamento diminuiu ao longo do gradiente de temperatura. Para entender o efeito da disponibilidade de alimento sobre a expressão de características morfológicas em cada um dos sexos, manipulamos a dieta durante o desenvolvimento de indivíduos provenientes de uma população de clima tropical e uma de clima temperado. Independente da população, o dimorfismo sexual foi causado por diferenças sexuais na dependência de condição. Machos e fêmeas diferiram não apenas na magnitude da resposta, mas também na direção. Em relação ao comprimento relativo dos fórceps, em particular, os resultados obtidos em laboratório não apóiam que a variação encontrada em campo se deve à disponibilidade de alimento. Outros fatores que não levamos em consideração, tais como densidade populacional, podem exercer um papel importante na resposta de machos e fêmeas em relação ao tamanho do armamento. Por fim, mais estudos experimentais comparando populações com diferenças marcantes de condições ambientais poderão lançar luz sobre quais fatores ecológicos podem ter favorecido a evolução do dimorfismo sexual dependente de condiçãoSexual dimorphism varies considerably among populations within species. This variation in the direction and magnitude of sexual dimorphism is partially explained by sexual differences in phenotypically plastic responses to environmental conditions and resource availability. Laboratory experiments have already shown that temperature and food availability are important factors promoting inter-individual morphological variation and that their effects differ between males and females. We used individuals of the earwig Labidura xanthopus (Dermaptera) collected from 20 Brazilian localities to investigate how body size and weapon size of males and females vary across a natural temperature gradient. Body size decreased with increasing temperature, but sexual size dimorphism remained constant across the temperature gradient. For weapon size, we found a negative relationship for males and a positive relationship for females. Thus, the magnitude of sexual dimorphism in weapon size decreased across the temperature gradient. To understand the effect of food availability on the expression of morphological traits in each sex, we manipulated the diet of individuals from a tropical and temperate population. Regardless of the population, sexual dimorphism was caused by sex-differences in condition dependence. Males and females differed not only in the magnitude of their responses, but also in the direction. Regarding the relative length of the forceps, in particular, our results do not support the interpretation that the morphological variation observed in the field is explained by differences in food availability. Other factors not considered here, such as population density, may play an important role in determining weapon size variation in males and females under natural conditions. Finally, more experimental studies comparing populations with marked differences in environmental conditions may shed light on which ecological factors have favored the evolution of condition-dependent sexual dimorphis

Adhesive secretions in harvestmen (Arachnida : Opiliones)

Opiliones, colloquially also known as harvestmen or daddy longlegs, are arachnids capable of producing and releasing a variety of secretions that are used to deter predators. The fact that a large fraction of these animals also produce efficient glues for trapping prey, gluing eggs to substrates, attaching soil particles to their body or eggs for camouflage purposes, or transferring sperm, is rather unknown. Not only the physical properties of these glues are interesting, but also the supplementary cuticular structures, that work hand in hand with the secretions to produce highly efficient adhesive mechanisms. Here we give an overview on the occurrence, properties, and associated structures of adhesive secretions in harvestmen and discuss their biological functions.21 page(s

Scorpion sheds 'tail' to escape: consequences and implications of autotomy in scorpions (Buthidae: Ananteris)

Autotomy, the voluntary shedding or detachment of a body part at a determined cleavage plane, is a common anti-predation defense mechanism in several animal taxa, including arthropods. Among arachnids, autotomy has been observed in harvestmen, mites, and spiders, always involving the loss of legs. Autotomy of the opisthosoma (abdomen) was recently reported in a single species of the Neotropical buthid scorpion genus Ananteris Thorell, 1891, but few details were revealed. Based on observations in the field and laboratory, examination of material in museum collections, and scanning electron microscopy, we document autotomy of the metasoma (the hind part of the opisthosoma, or ?tail?) in fourteen species of Ananteris. Autotomy is more common in males than females, and has not been observed in juveniles. When the scorpion is held by the metasoma, it is voluntarily severed at the joints between metasomal segments I and II, II and III, or III and IV, allowing the scorpion to escape. After detachment, the severed metasoma moves (twitches) automatically, much like the severed tail of a lizard or the severed leg of a spider, and reacts to contact, even attempting to sting. The severed surface heals rapidly, scar tissue forming in five days. The lost metasomal segments and telson cannot be regenerated. Autotomy of the metasoma and telson results in permanent loss of the posterior part of the scorpion?s digestive system (the anus is situated posteriorly on metasomal segment V) and the ability to inject venom by stinging. After autotomy, scorpions do not defecate and can only capture small prey items. However, males can survive and mate successfully for up to eight months in the laboratory. In spite of diminished predation ability after autotomy, survival allows males to reproduce. Autotomy in Ananteris therefore appears to be an effective, adaptive, anti-predation escape mechanism.Fil: Mattoni, Camilo Ivan. Universidad Nacional de Córdoba; ArgentinaFil: García Hernández, Solimary. Universidad Industrial Santander; Colombia. Universidade de Sao Paulo; BrasilFil: Botero Trujillo, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina. Pontificia Universidad Javeriana; ColombiaFil: Ochoa, José A.. Frankfurt Zoological Society; Perú. Universidade de Sao Paulo; BrasilFil: Ojanguren Affilastro, Andres Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Pinto da rocha, Ricardo. Universidade de Sao Paulo; BrasilFil: Prendini, Lorenzo. American Museum Of Natural History; Estados Unido

Post-autotomy healing of severed stump of metasomal segment of adult male <i>Ananteris solimariae</i> Botero-Trujillo & Flórez, 2011.

<p>A. One hour after autotomy, with drop of hemolymph. B. One day after, hemolymph loss continues. C. Two days after, hemolymph loss reduced, brown scar beginning to develop. D. Three days after, hemolymph loss reduced, scar developing. E. Four days after, scar almost completely developed. F. Five days after, no hemolymph loss, scar fully formed. G. Ten days after, scar darkened. H. Twenty-five days after, scar fully defined.</p

<i>Ananteris solimariae</i> Botero-Trujillo & Flórez, 2011, adult males, twenty-five days after autotomy.

<p>A. Feeding on cricket nymph. B. Attempting to sting, showing swollen opisthosoma. C. Accumulated excrement evident as white area inside opisthosoma (arrow).</p

Scanning electron micrographs of cleavage planes on severed stumps of metasomal segments of selected buthid scorpions.

<p>A, B. <i>Ananteris balzani</i> Thorell, 1891, segments III, posterior end (A) and IV, anterior end (B), manipulated with forceps to induce detachment. C, D. <i>Zabius fuscus</i> (Thorell, 1876), segments II, posterior end (C) and III, anterior end (D), detached with forceps. E, F. <i>Ananteris solimariae</i> Botero-Trujillo & Flórez, 2011, segments III, posterior end (E) and IV, anterior end (F), post-autotomy. Scale bars = 0.5 mm.</p

Incidence of metasomal autotomy in wild populations of the scorpion genus <i>Ananteris</i> Thorell, 1891 (Buthidae).

<p>Count of specimens collected with part of metasoma detached and with a well-developed scar on the severed stump (parentheses). No adult females or immatures were observed with a well-developed scar on the severed stump of the metasoma.</p><p>Incidence of metasomal autotomy in wild populations of the scorpion genus <i>Ananteris</i> Thorell, 1891 (Buthidae).</p

Autotomy in <i>Ananteris</i> Thorell, 1891 scorpions.

<p>A. <i>Ananteris balzani</i> Thorell, 1891, adult male from Serra das Araras Ecological Station, Mato Grosso State, Brazil. Dashed lines indicate autotomy cleavage planes between metasomal segments I-IV. B, C. Autotomy in <i>Ananteris solimariae</i> Botero-Trujillo & Flórez, 2011, adult male, video frames. B. Exact moment before autotomy, scorpion fighting to escape. Arrow indicates beginning of cleavage. C. Immediately after autotomy, detached tail twitching.</p

Records of metasomal autotomy in scorpions of the genus <i>Ananteris</i> Thorell, 1891 (Buthidae).

<p>L = autotomy observed in the laboratory; F = autotomy observed in the field; S = collected with a well-developed scar on the severed stump of the metasoma.</p><p>* Some data about detached segments are missing.</p><p>Records of metasomal autotomy in scorpions of the genus <i>Ananteris</i> Thorell, 1891 (Buthidae).</p