Reproductive biology of harvestmen (Arachnida: Opiliones): a review of a rapidly evolving research field.

Harvestmen are a major arachnid order that has experienced a dramatic increase in biological knowledge in the 21st century. The publication of the book Harvestmen: The Biology of Opiliones in 2007 stimulated the development of many behavioral studies. Although the book is relatively recent, our understanding of the reproductive biology of harvestmen is already outdated due to the fast accumulation of new data. Our goal is to provide an updated review of the subject to serve as a benchmark for the following years. In the pre-copulatory phase, we explore the evolution of facultative parthenogenesis, the factors that may affect the types of mating system, and the role of nuptial gifts in courtship. Regarding the copulatory phase, harvestmen are unique arachnids because they have aflagellate spermatozoa and a penis with complex morphology. We discuss the implications of these two features for sperm competition and cryptic female choice. In the post-copulatory phase, we connect oviposition site selection and climate conditions to the widespread occurrence of resource defense polygyny, alternative reproductive tactics, and sexual dimorphism in several clades of tropical harvestmen. Finally, we present the different forms of parental care in the order, and discuss the benefits and costs of this behavior, which can be performed either by females or males. Throughout the review, we indicate gaps in our knowledge and subjects that deserve further studies. Hopefully, the information synthesized here will stimulate researchers worldwide to embrace harvestmen as a study system and to improve our effort to unravel the mysteries of their reproductive biology.

Benefits and costs of female and male care in amphibians: a meta-analytical approach.

The origin of parental care is a central question in evolutionary biology, and understating the evolution of this behaviour requires quantifying benefits and costs. To address this subject, we conducted a meta-analysis on amphibians, a group in which parental care has evolved multiple times. We found that both male and female parents increase egg survival, regardless of whether the breeding site is concealed or exposed. Parental care also increases survival and growth of tadpoles and juveniles, independent of the caring sex. However, parental care reduces parental body condition, particularly when parents remain stationary near the offspring. Females tend to experience higher reproductive costs, but sample size is restricted to few species. In some frog species, paternal care increases male reproductive success because females prefer caring males. The benefits of parental care in amphibians resembles those reported for arthropods but differ from fish, in which parental care does not improve offspring survival. Moreover, the decrease in body condition, which is not found in fish, is influenced by the form of parental care, suggesting a trade-off between caring and foraging, as already reported for certain arthropods. Finally, the reproductive costs of parental care for both sexes remain unexplored and deserve further research.

Juvenile leg autotomy predicts adult male morph in a New Zealand harvestman with weapon polymorphism.

Intraspecific weapon polymorphisms that arise via conditional thresholds may be affected by juvenile experience such as predator encounters, yet this idea has rarely been tested. The New Zealand harvestman Forsteropsalis pureora has three male morphs: majors (alphas and betas) are large-bodied with large chelicerae used in male-male contests, while minors (gammas) are small-bodied with small chelicerae and scramble to find mates. Individuals use leg autotomy to escape predators and there is no regeneration of the missing leg. Here, we tested whether juvenile experience affects adult morph using leg autotomy scars as a proxy of predator encounters. Juvenile males that lost at least one leg (with either locomotory or sensory function) had a 45 times higher probability of becoming a minor morph at adulthood than intact juvenile males. Leg loss during development may affect foraging, locomotion, and/or physiology, potentially linking a juvenile's predator encounters to their final adult morph and future reproductive tactic.

Function of a multimodal signal: A multiple hypothesis test using a robot frog.

Multimodal communication may evolve because different signals may convey information about the signaller (content-based selection), increase efficacy of signal processing or transmission through the environment (efficacy-based selection), or modify the production of a signal or the receiver's response to it (inter-signal interaction selection). To understand the function of a multimodal signal (aggressive calls + toe flags) emitted by males of the frog Crossodactylus schmidti during territorial contests, we tested two hypotheses related to content-based selection (quality and redundant signal), one related to efficacy-based selection (efficacy backup), and one related to inter-signal interaction selection (context). For each hypothesis we derived unique predictions based on the biology of the study species. In a natural setting, we exposed resident males to a robot frog simulating aggressive calls (acoustic stimulus) and toe flags (visual stimulus), combined and in isolation, and measured quality-related traits from males and local levels of background noise and light intensity. Our results provide support to the context hypothesis, as toe flags (the context signal) are insufficient to elicit a receiver's response on their own. However, when toe flags are emitted together with aggressive calls, they evoke in the receiver qualitatively and quantitatively different responses from that evoked by aggressive calls alone. In contrast, we found no evidence that toe flags and aggressive calls provide complementary or redundant information about male quality, which are key predictions of the quality and redundant signal hypotheses respectively. Finally, the multimodal signal did not increase the receiver's response across natural gradients of light and background noise, a key prediction of the efficacy backup hypothesis. Toe flags accompanying aggressive calls seem to provide contextual information that modify the receiver's response in territorial contests. We suggest this contextual information is increased motivation to escalate the contest, and discuss the benefits to the signallers and receivers of adding a contextual signal to the aggressive display. Examples of context-dependent multimodal signals are rare in the literature, probably because most studies focus on single hypotheses assuming content- or efficacy-based selection. Our study highlights the importance of considering multiple selective pressures when testing multimodal signal function.

Short- and long-term effects of an extreme case of autotomy: does "tail" loss and subsequent constipation decrease the locomotor performance of male and female scorpions?

In many taxa, individuals voluntarily detach a body part as a form to increase their chances of escaping predation. This defense mechanism, known as autotomy, has several consequences, such as changes in locomotor performance that may affect fitness. Scorpions of the genus Ananteris autotomize the "tail", which in fact corresponds to the last abdominal segments. After autotomy, individuals lose nearly 25% of their body mass and the last portion of the digestive tract, including the anus, which prevents defecation and leads to constipation, because regeneration does not occur. Here, we experimentally investigated the short- and long-term effects of tail loss on the locomotor performance of Ananteris balzani. In a short-term experiment, the maximum running speed (MRS) of males and females did not change after autotomy. Moreover, the relative mass of the lost tail did not affect the change in MRS after autotomy. In a long-term experiment, autotomy had a negative effect on the MRS of males, but not of females. Autotomized over-fed individuals suffered from severe constipation but were not slower than autotomized normally fed individuals. In conclusion, tail loss has no immediate effect on the locomotor performance of scorpions. The long-term decrease in the locomotor performance of autotomized males may impair mate searching. However, because death by constipation takes several months, males have a long time to find mates and reproduce. Thus, the prolonged period between autotomy and death by constipation is crucial for understanding the evolution of one of the most extreme cases of autotomy in nature.

Müllerian mimicry between oil-producing orchids and Malpighiaceae? An old hypothesis finally tested.

The concept of mimicry has been developed for animals, but it also applies to plants. Plant species may be Müllerian mimics if they have similar reproductive traits and offer similar rewards to the pollinators. Several Oncidiinae orchids offer floral oils to their pollinators and have been suggested to form a Müllerian complex with species of Malpighiaceae. We provide a test of this hypothesis using Gomesa flexuosa (Orchidaceae) and Janusia guaranitica (Malpighiaceae), which are sympatric and phenologically synchronous, secrete the same floral resource (oils), and show similar flower morphology. We exposed individuals of Gomesa near and far from individuals of Janusia and monitored floral visitation. Both species were exclusively pollinated by oil-collecting bees, sharing Centris trigonoides as a pollinator. Nevertheless, the probability of bee visitation, number of contact approximations, and number of visits to flowers of Gomesa were similar when individuals were near and far from Janusia. These findings do not support the Müllerian mimicry hypothesis in these two species. Their resemblances can be better explained by the "exploitation of perceptual biases" hypothesis. According to this hypothesis, pre-existing traits in Oncidiinae orchids (e.g. colour, shape, rewards) may coopt oil-collecting bees that usually search for rewards in Malpighiaceae species with similar flower traits.

Differential allocation in a gift-giving spider: males adjust their reproductive investment in response to female condition.

BACKGROUND: When males are selective, they can either reject low-quality females or adjust their reproductive investment in response to traits that indicate female quality (e.g., body size or condition). According to the differential allocation hypothesis, males increase their reproductive investment when paired with high-quality females (positive differential allocation) or increase their reproductive investment when paired with low-quality females (negative differential allocation). This hypothesis has been proposed for monogamous species with biparental care, and most empirical studies focus on birds. Here we used the polygamous spider Paratrechalea ornata, in which males offer prey wrapped in silk as nuptial gifts, to test whether males adjust their reproductive investment in gift size, pre-copulatory and copulatory courtship, and sperm transfer in response to female body condition. RESULTS: Males exposed to females in good body condition added more flies to the gift, stimulated these females longer with abdominal touches during pre-copulatory courtship, and had longer pedipalp insertions than males exposed to females in poor body condition. Female condition affected neither silk investment in nuptial gift wrapping nor the quantity of sperm transferred by males. Finally, females in good body condition oviposited faster after copulation and laid more eggs than females in poor body condition. CONCLUSIONS: We provide experimental evidence that males of a gift-giving spider exhibit positive differential allocation in three key aspects of their reproductive investment: the size of the nutritious gift, duration of pre-copulatory courtship, and duration of pedipalp insertions, which is regarded as a form of copulatory courtship in spiders. This positive differential allocation is likely associated with the benefits of copulating with females in good body condition. These females are more fecund and oviposit faster after copulation than females in poor body condition, which under natural field conditions probably reduces the risk of multiple matings and thus the level of sperm competition faced by the males. As a final remark, our findings indicate that the hypothesis of differential allocation also applies to species with a scramble competition mating system, in which males heavily invest in nuptial gift construction, but not in parental care.

It is not always about body size: evidence of Rensch's rule in a male weapon.

In many species, sexual dimorphism increases with body size when males are the larger sex but decreases when females are the larger sex, a macro-evolutionary pattern known as Rensch's rule (RR). Although empirical studies usually focus exclusively on body size, Rensch's original proposal included sexual differences in other traits, such as ornaments and weapons. Here, we used a clade of harvestmen to investigate whether two traits follow RR: body size and length of the fourth pair of legs (legs IV), which are used as weapons in male-male fights. We found that males were slightly smaller than females and body size did not follow RR, whereas legs IV were much longer in males and followed RR. We propose that sexual selection might be stronger on legs IV length than on body size in males, and we discuss the potential role of condition dependence in the emergence of RR.

Fitness Implications of Nonlethal Injuries in Scorpions: Females, but Not Males, Pay Reproductive Costs.

AbstractThe ability to detach a body part in response to a predation attempt is known as autotomy, and it is perhaps the most intensively studied form of nonlethal injury in animals. Although autotomy enhances survival, it may impose reproductive costs on both males and females. We experimentally investigated how autotomy affects the reproductive success of males and females of a scorpion species. Individuals of Ananteris balzani autotomize the last abdominal segments (the tail), losing the anus and leading to lifelong constipation, since regeneration does not occur. Although the male tail is used during courtship and sperm transfer, autotomy has no effect on male mating success. The combined effect of increased mortality and reduced fecundity resulted in autotomized females producing nearly 35% fewer offspring than intact females. In conclusion, the negative effects of tail autotomy are clearly sex dependent, probably because the factors that influence reproductive success in males and females are markedly different.

Colonization of novel algal habitats by juveniles of a marine tube-dwelling amphipod.

BACKGROUND: Dispersal is an important process affecting population dynamics and connectivity. For marine direct developers, both adults and juveniles may disperse. Although the distribution of juveniles can be initially constrained by their mothers' choice, they may be able to leave the parental habitat and colonize other habitats. We investigated the effect of habitat quality, patch size and presence of conspecific adults on the colonization of novel habitats by juveniles of the tube-dwelling amphipod Cymadusa filosa associated with the macroalgal host Sargassum filipendula. METHODS: We tested the factors listed above on the colonization of juveniles by manipulating natural and artificial plants in both the field and laboratory. RESULTS: In the laboratory, juveniles selected high-quality habitats (i.e., natural alga), where both food and shelter are provided, when low-quality resources (i.e., artificial alga) were also available. In contrast, habitat quality and algal patch size did not affect the colonization by juveniles in the field. Finally, the presence of conspecific adults did not affect the colonization of juveniles under laboratory condition but had a weak effect in the field experiment. Our results suggest that C. filosa juveniles can select and colonize novel habitats, and that such process can be partially affected by habitat quality, but not by patch size. Also, the presence of conspecifics may affect the colonization by juveniles. Successful colonization by this specific developmental stage under different scenarios indicates that juveniles may act as a dispersal agent in this species.

Within-population variation in female mating preference affects the opportunity for sexual selection and the evolution of male traits, but things are not as simple as expected.

Females from the same population usually have phenotypic variation in their mating preferences. However, the effects of this within-population variation on the sexual selection acting on males are still unclear. We used individual-based models to explore how within-population variation in female preference (i.e. which male trait value is preferred) and preference strength (i.e. how strong the preference is) affects the opportunity for sexual selection (Is ) and the evolution of a sexually selected male trait. We found the highest Is values when females had high variation in preference and an open-ended preference function. The lowest Is occurred when the magnitude of variation in female preference and male trait value were the same and preference function was closed. Male trait exaggeration was higher when there was high within-population variation in preference and females had an open-ended preference function. Also, higher male trait variation was maintained by high variation in preference, but only for a closed preference function. Thus, we found that only within-population variation in female preference, not in preference strength, influences the opportunity for sexual selection and the evolution of sexually selected male traits. Moreover, we found that the shape of the preference function (i.e. open-ended or closed) and the magnitude of within-population variation in female preference compared to male trait variation also influences the Is and consequently the evolution of male traits.

Echocardiographic Study of the Coronary Sinus in the Indeterminate Form of Chagas Disease.

INTRODUCTION: We investigated the occurrence of coronary sinus abnormalities in the indeterminate form of Chagas disease (CD). METHODS: Differences between the maximum and minimum diameters of the coronary sinus (∆%) on echocardiography were evaluated in individuals with the indeterminate form of CD (n=14) and those without (n=16) CD. The association of the difference with abnormalities detected by echocardiography and myocardial scintigraphy was assessed. RESULTS: The mean Δ% values did not differ significantly between the groups. There was no correlation of the measurements with echocardiographic and myocardial scintigraphy findings. CONCLUSIONS: The coronary sinus evaluation revealed no differences between the groups.

Echocardiographic Study of the Coronary Sinus in the Indeterminate Form of Chagas Disease

Abstract INTRODUCTION: We investigated the occurrence of coronary sinus abnormalities in the indeterminate form of Chagas disease (CD). METHODS: Differences between the maximum and minimum diameters of the coronary sinus (∆%) on echocardiography were evaluated in individuals with the indeterminate form of CD (n=14) and those without (n=16) CD. The association of the difference with abnormalities detected by echocardiography and myocardial scintigraphy was assessed. RESULTS: The mean Δ% values did not differ significantly between the groups. There was no correlation of the measurements with echocardiographic and myocardial scintigraphy findings. CONCLUSIONS: The coronary sinus evaluation revealed no differences between the groups.

Nutrition of marine mesograzers: integrating feeding behavior, nutrient intake and performance of an herbivorous amphipod.

Consumers can regulate the acquisition and use of nutrients through behavioral and physiological mechanisms. Here, we present an experimental approach that simultaneously integrates multiple nutritional traits, feeding assays, and juvenile performance to assess whether a marine herbivore (the amphipod Ampithoe valida) regulates the intake of elements (carbon and nitrogen), macronutrients (protein and non-protein) or both when offered freeze-dried tissues of seaweeds varying in nutritional content. We assessed behavioral regulation of nutrients in three ways. First, during no-choice assays, we found that amphipods ingested similar amounts of carbon, but not nitrogen, non-protein and protein, across algal diets. Second, herbivore intake rates of carbon, protein and non-protein components across no-choice assays was similar to intake rates when offered a choice of foods. Third, variation in intake rates of carbon and non-protein components among algal diets was significantly greater than was tissue content of these components, while variation in intake rates of nitrogen was significantly lower; differences in protein intake variation was equivocal. While these analytical approaches are not uniformly consistent, carbon and nitrogen seem to emerge as the nutrient components that are more strongly regulated by A. valida. Juveniles reared on single diets shown patterns of survivorship, growth and reproduction that could not be predicted by these feeding preferences, nor nutrient content. We conclude that an integrative approach that considers the intake of multiple nutrients potentially yields insights into feeding behavior and its performance consequences.

Do the species with facies reclinobunoides make up a clade?-A new Lomanius (Opiliones, Podoctidae) from Vietnam and a discussion on its relationships.

Lomanius annae sp. nov. is described from southern Vietnam. The species is characterized by the greatly developed dorso-basal process on cheliceral hand of males and by the partial effacement of all mesotergal grooves. The genus Lomanius contains four generic synonyms and currently comprises eight valid species distributed in China, Java, peninsular Malaysia, the Philippines, and Taiwan. The new species displays a general morphology similar to the former genus Paralomanius, with a combination of sexually dimorphic interocular mound (which is very large and strongly leaned back in males) and pedipalpus (which is extremely elongate in males). This morphological suite of features is herein called facies reclinobunoides. The replacement name Metibalonius triceratops nom. nov. is proposed for Trispinibunus abnormis Roewer, 1915, which is a junior secondary homonym of Ibalonius abnormis Strand, 1911. Finally, numerous morphological structures found in Podoctidae are recognized and named: (1) the cheliceral comb, present on cheliceral fingers, (2) the chained tubercular ridges, present on dorsal scutum and (3) several others related to the ocular region. The distribution of these two structures among podoctid species is not fully known, but both are absent in the former Ibaloniinae. We suggest that both structures may be useful to define supra-generic groups in the clade composed of the former Podoctinae and Erecananinae.

Males, but not females, perform strategic mate searching movements between host plants in a leaf beetle with scramble competition polygyny.

Mate searching is assumed to be performed mostly by males, but when females benefit from multiple mating or are under risk of failing to mate, they may also perform mate searching. This is especially important in scramble competition polygynies, in which mate searching is the main mechanism of mate competition. Typically, more mobile individuals are expected to achieve higher mating success because mobility increases their probability of finding mates. If we assume individual movements are mainly explained by mate searching in scramble competition polygynies, we can investigate searching strategies by asking when individuals should leave their location and where they should go. We hypothesize that individuals will leave their locations when mating opportunities are scarce and will seek spatially close sites with better mating opportunities. We tested these hypotheses for males and females of Leptinotarsa undecimlineata, a leaf beetle with scramble competition polygyny in which both sexes are promiscuous. Individuals mate and feed exclusively on Solanum plants, and thus, individual movements can be described as switches between plants. Females were less likely than males to leave isolated plants, and both males and females moved preferentially to neighboring plants. Males were more likely to leave when the local number of females was low, and the number of males was high. They moved to plants with more females, a behavior consistent with a mate searching strategy. Females were more likely to move to plants with fewer males and many females, a behavior consistent with male harassment avoidance. Strategic movement is widely considered in foraging context, but seldom in a mate searching context. Considering that selection to minimize searching costs, maximize mating success, and minimize harassment may be ubiquitous in nature, we argue that strategic movements by mate searching individuals are likely to occur in many species.

Mate sampling influences the intensity of sexual selection and the evolution of costly sexual ornaments.

Mate choice includes three steps: (1) a choosing individual encounters potential mates, (2) assesses and processes information about them, and (3) makes a mate decision. During mate searching females can access only a sample of males in the mating pool and need to choose their mates based on limited information. Thus, mate sampling may influence sexual selection promoted by mate choice because it constrains female choice. Using individual-based simulations, we found that both female choosiness and mate sampling influenced the variance in mating success among males and thus the intensity of sexual selection. So that sexual selection is most intense when females are strongly choosy and can sample many males. Moreover, in evolutionary simulations, the rate of evolutionary change and the final size of male ornament increase with increasing mate sampling. However, under stronger natural selection, evolutionary change is slower and leads to smaller ornaments. Empirical data on the potential for sexual selection (Is) for several animal species show a positive correlation between the intensity of sexual selection and an index of mate sampling based on behavioral and ecological traits. Based on the results of our simulations, we predict that males of highly mobile species with long-range sexual signal transmission, which allow females to assess many males, will show greater variance in mating success and will be more ornamented than their relatives not exhibiting these features.

The assassination of a hypothesis by non-critical interpretation of molecular data: A comment on.

In a recent paper, Sharma et al. (2017) tested the hypothesis that eggs attached to males' legs in podoctid harvestmen are laid by conspecifics. Using molecular methods, they falsify the "paternal care hypothesis" and suggest that the eggs belong to spiders. Here we raise several criticisms to the authenticity of this finding and present arguments supporting the hypothesis that eggs belong to harvestmen and are not accidentally attached to the males. We argue that the falsification of the paternal care hypothesis in podoctids is premature and based on non-critical interpretation of molecular data.

Macroecology of parental care in arthropods: higher mortality risk leads to higher benefits of offspring protection in tropical climates.

The intensity of biotic interactions varies around the world, in such a way that mortality risk imposed by natural enemies is usually higher in the tropics. A major role of offspring attendance is protection against natural enemies, so the benefits of this behaviour should be higher in tropical regions. We tested this macroecological prediction with a meta-regression of field experiments in which the mortality of guarded and unguarded broods was compared in arthropods. Mortality of unguarded broods was higher, and parental care was more beneficial, in warmer, less seasonal environments. Moreover, in these same environments, additional lines of defence further reduced offspring mortality, implying that offspring attendance alone is not enough to deter natural enemies in tropical regions. These results help to explain the high frequency of parental care among tropical species and how biotic interactions influence the occurrence of parental care over large geographic scales. Finally, our findings reveal that additional lines of defences - an oftentimes neglected component of parental care - have an important effect on the covariation between the benefits of parental care and the climate-mediated mortality risk imposed by natural enemies.

Chemical Defense as a Condition-Dependent Trait in Harvestmen.

The expression of costly traits often depends on the amount of food available to the individuals. Chemical defenses are costly, thus their production should be condition-dependent. Here, we tested the hypothesis that an increase in food availability and an acetate-supplemented diet will increase the production of chemical defenses by the harvestman Magnispina neptunus, which releases alkylated benzoquinones biosynthesized using acetate as a precursor. We manipulated the diet of the individuals and created four experimental groups: well-fed with acetate, well-fed without acetate, poorly-fed with acetate, and poorly-fed without acetate. Well-fed individuals produced secretions with higher mass and concentration of benzoquinones than poorly-fed individuals, but we detected no significant effect of the acetate supplement. Thus, the production of benzoquinones is condition-dependent, and even short periods of dietary restriction may make individuals more vulnerable to predators, imposing fitness consequences to chemically-protected arthropods that biosynthesize their own defensive compounds.