Victor R. Townsend

The interaction of temperature, dissolved oxygen and predation pressure in an aquatic predator-prey system

We examined the effects of the physical environment on the outcome of predatory encounters between tadpoles of the frog Rana clamitans and the fishing spider, Dolomedes triton. These species co-occur in pond habitats that vary widely in dissolved oxygen and temperature. Water temperature and oxygen levels have complex effects on the behavior of anuran larvae. Behavioral responses induced by shifting physiological requirements can increase the risk of predation on tadpoles. We experimentally manipulated treatment levels of both dissolved oxygen and temperature in trials conducted between individual predators (Dolomedes) and single prey (Rana). Environmental conditions had significant effects on the behavior of tadpoles that increased the risk of attack by Dolomedes. Under the low oxygen condition, more tadpoles were eaten, and the total amount of time spent at the surface and the number of times surfaced per minute were significantly greater. For Dolomedes, increased tadpole activity resulted in the increased expression of several predatory behaviors. We found significant treatment and interaction effects on the expression of both resting and ambush postures. In addition, survival analyses showed a significantly earlier expression of predatory behaviors in decreased oxygen level treatments.

Diversity and Habitat Use of Neotropical Harvestmen (Arachnida: Opiliones) in a Costa Rican Rainforest

In tropical rain forests, harvestmen assemblages are extremely diverse, with richness often exceeding 25 species. In the neotropics, there are published accounts of harvestmen faunas in South America rainforests (especially Amazonia), but relatively little is known about the community ecology of harvestmen in tropical forests of Central America. In this paper, we provide the first insights into the diverse assemblage of harvestmen inhabiting a wet forest at La Selva Biological Station, Costa Rica. Over five field seasons, we recorded 38 species. During our 2009 field season, we examined variation in species abundance, richness, and composition between adjacent successional forests (young secondary, mature secondary, and primary forests) as well as between distinct habitats (ground/litter layer and shrub/tree layer). Based on night samples (but not day), our results indicate that there are only minor differences in species composition and relative abundance between the forest ages, but no differences in richness. The ground/litter layer and shrub/tree layer habitats differed markedly in species composition, species richness, and relative abundance of several species. Our analysis of covariance supports the hypothesis that leg length is related to climbing behavior for several species belonging to Eupnoi and Laniatores.

Activity Patterns of Two Species of Neotropical Harvestmen (Arachnida: Opiliones) from Costa Rica

ABSTRACT Natural history studies serve as important foundations for future investigations of behavioral ecology and provide biologists with critical information needed for the development of empirical research programs. Relatively little is known about the biology of most species of Neotropical harvestmen in Central America. In this field study, we investigated the activity patterns of two common species Cynorta marginalis (Cosmetidae) and Prionostemma sp. (Sclerosomatidae) in a wet tropical forest in Costa Rica. We used visual encounter surveys along randomly selected transects to compare the relative abundance of these species during morning, afternoon, evening, and late night sampling periods. To generate ethograms, we observed up to three individuals of each species for 10 min along each transect, generating 69 behavioral observations for C. marginalis and 51 for Prionostemma. Both species occupy perches on vegetation and are generally nocturnal with respect to activity. After dusk, individuals of C. marginalis actively climb, interact with conspecifics, and forage on the surfaces of small and large trees. During the day, adult Prionostemma form relatively inactive clusters of up to 40 individuals on arboreal perches and descend to the leaf litter after dusk to forage.

Morphological Changes During Postembryonic Development in Two Species of Neotropical Harvestmen (Opiliones, Laniatores, Cranaidae)

Morphological changes during postembryonic development in the Cranaidae are described on the basis of the examination of an incomplete series of larvae, nymphs, and adults of Phareicranaus calcariferus and Santinezia serratotibialis. The life histories of these species are hypothesized to consist of six nymphal stages, featuring the appearance of secondary male sexual characteristics in the antepenultimate nymph (N5). Color and body shape change dramatically during development. Growth rates for nymphs based upon leg measurements were similar for both species. In S. serratotibialis, the greatest increase in leg size occurred from larva to 1st nymph. The tarsomeres of legs I–IV varied by 1–2 segments per leg for each nymph stage, with the number of tarsal segments increased by 1–2 segments at each stage. Adults had nearly twice as many tarsomeres on leg II than other legs. Ontogenetic changes were observed in the armature of the proximal cheliceral segment, ocularium, pedipalp, opisthosoma, distitarsus III and IV, and leg IV. Morphological changes in postembryonic development in cranaid harvestmen are similar to those reported for other Laniatores. J. Morphol., 2009.

Tree Use by Harvestmen (Arachnida: Opiliones) in the Rainforests of Trinidad, W. I.

Abstract. Relatively little is known about the microhabitat preferences of most species of Neotropical harvestmen. We investigated the use of trunks, buttresses, and the leaf litter in the immediate vicinity of trees by multiple species of harvestmen in a Trinidad, W. I. rainforest. A total of 238 individuals were collected. This included adults of species from the families Cosmetidae, Manaosbiidae, Sclerosomatidae, and Stygnidae. Our results indicate that the cosmetids (2 species), especially Cynortula sp., were the most abundant species to occur on the trees. We also found significant, positive correlations for several species with regard to tree size and the number of individuals present. We hypothesize that harvestmen may use the surfaces of trees as well as the leaf litter in the immediate vicinity of the buttresses as either shelters from potential predators or as areas that provide favorable microclimates (e.g., relatively high humidity).

Ultrastructure of the cuticular scales of lynx spiders (Araneae, Oxyopidae) and jumping spiders (Araneae, Salticidae)

The cuticular scales of spiders are flattened setae that may occur in a diverse array of colors and shapes on the dorsal and lateral surfaces of the prosoma, opisthosoma, and walking legs. In this study, we used transmission electron microscopy (of both sections and wholemounts) and scanning electron microscopy (in concert with paraffin carving) to examine the internal anatomy and ultrastructure of the cuticular scales of several species of lynx spiders (Oxyopidae) and jumping spiders (Salticidae). We also examined iridescent and noniridescent pigmented scales for species in both families. In addition to discovering intra‐ and interspecific and sexual differences in scale ultrastructure, the results of our research also indicate that the ultrastructure of the scales of these spiders varies directly with coloration. For iridescent scales, we found a general absence of trabeculae, a lack of pigment granules, and an almost complete fusion of the the upper and lower laminae. For noniridescent scales, we observed granules, well‐formed trabeculae, and a complex internal structure consisting of internal elements within the lumen of the scale. Our examination of the scales of these spiders represents the first complete description of the ultrastructure of the cuticular scales of any species of spider. J. Morphol. 240:77–92, 1999.

The Ecological Significance of Leg Autotomy for Climbing Temperate Species of Harvestmen (Arachnida, Opiliones, Sclerosomatidae)

Abstract In encounters with predators, sclerosomatid harvestmen may employ a variety of defensive tactics including the voluntary detachment of legs (autotomy). The long-term costs of this evasive defense are not fully understood, but prior studies have documented negative consequences for terrestrial locomotion and foraging. In this study, we investigated the impact of leg loss upon locomotion in adult harvestmen (Leiobunum spp.). In southeastern Virginia, these harvestmen regularly climb vegetation and occupy perches on tree trunks, branches, and leaves that are often 1–2 m or more above the ground. In our study, we measured walking and climbing speeds for individuals with 5, 6, 7, and 8 legs. The results of our field surveys conducted over three seasons revealed relatively high frequencies (36–63%) of leg loss. We also found that individuals with six legs occupied perches that were significantly lower in the understory than those with eight legs. In the lab, we observed significantly slower walking speeds for individuals missing one or more legs. We also found that individuals with five legs climb significantly slower than individuals with eight legs. On the bases of the observed frequencies of leg loss in the field, we infer that leg autotomy is a common (and effective) evasive tactic used by harvestmen. However, the reduction in walking and climbing speeds resulting from leg loss may also affect habitat selection, (e.g., perch height) and may ultimately reduce the survivorship of individuals in future encounters with predators.

Diversity of Neotropical Harvestmen (Arachnida: Opiliones) Inhabiting Logs and Palm Fronds in the Rain Forests of Trinidad

ABSTRACT In July and August 2005, we investigated the use of two distinct microhabitats by harvestmen (Arachnida: Opiliones) in crappo-cocorite seasonal forest, lower montane rain forest, and upper montane rain forest of the Northern Range of Trinidad, West Indies. In addition to new locality records, geographic distributions, and microhabitat use, this article provides a preliminary understanding of the species diversity, compositional similarity, and relative harvestmen abundance among forest stands located within three types of rain forest of different altitudes found in Trinidad. We collected harvestmen inhabiting the space within and underneath decaying logs as well as the leaf litter associated with the logs. In upper montane rain forest, in addition to logs, we sampled the sheaths of palm (Euterpe broadwayi Becc. ex Broadway) fronds, another shelter commonly used by harvestmen that was especially abundant at the higher elevations. We collected 173 individuals representing eight families and 14 species. The number of harvestmen per shelter varied from 3.2 individuals per log in crappo-cocorite forest to 0.8 individual per log or palm frond sheath in upper montane rain forest. In the crappo-cocorite seasonal forest, cosmetids, sclerosomatids and stygnids were most abundant. In upper montane rain forest, cranaids and manaosbiids were the most abundant taxa, whereas cosmetids and sclerosomatids were relatively rare. Crappo-cocorite and lower montane forests were very similar in species composition but differed greatly from upper montane forest. The cosmetids Paecilaema inglei Goodnight and Goodnight 1947, Cynortula granulata Roewer 1912, and the stygnid Stygnoplus clavotibialis (Goodnight and Goodnight 1947) were found to be strongly correlated with the crappo-cocorite and lower montane forests, whereas in upper montane forests Santinezia serratotibialis Roewer 1932 and Cranellus montgomeryi Goodnight and Goodnight 1947 were closely correlated.

Interspecific variation in the microanatomy of cosmetid harvestmen (Arachnida, Opiliones, Laniatores)

Scanning electron microscopy (SEM) is a useful tool for identifying interspecific variation in often overlooked structures that may represent useful sources for informative phylogenetic characters. In this study, we used SEM to compare the morphology of 12 cosmetid species from Central America, the Caribbean, and North America including multiple species for the genera Cynorta, Erginulus, and Paecilaema. To determine if microanatomical structures were unique to the cosmetid taxa under examination, we investigated the microanatomical structures of six additional species of gonyleptoidean harvestmen representing the families Agoristenidae, Cranaidae, Gonyleptidae, Manaosbiidae, and Stygnidae. Our results indicate that the shape of the ocularium (narrow, intermediate, or broad) did not vary within cosmetid genera, whereas the morphology of the rough pit glands on the eye mound varied considerably between species. Each cosmetid species had 10–20 rough pit glands on the ocularium whereas only the eye mounds of Avima intermedia (Agoristenidae) and Glysterus sp. (Gonyleptidae) had similar structures. With regards to the surface texture of the dorsal scutum, cosmetid harvestmen exhibited a rivulose‐microgranulate morphology (6 species), a microtuberculate‐rivulose‐microrgranulate morphology (4 species), or a microgranulate morphology (2 species). In contrast, each of the gonyleptoidean species exhibited a microgranulate pattern, with the exception of Stygnoplus clavotibialis, which had a rivulose‐microgranulate surface texture. For cosmetid harvestmen, we observed considerable interspecific variation in the shape and number of teeth on the fixed and moveable fingers of the male chelicerae. Similarly, we also observed interspecific variation in the distribution and shape of tubercles on the ventral and dorsal surfaces of the femur of the pedipalp. Overall, our results indicate that there are several microanatomical structures associated with the ocularium, dorsal scutum, male chelicera, and pedipalp that could represent informative phylogenetic characters in future taxonomic studies of cosmetid harvestmen. J. Morphol. 275:1386–1405, 2014.

Reproductive morphology of three species of neotropical harvestmen (Opiliones, Laniatores, Gonyleptoidea)

Illustrations of penis morphology are essential components of species descriptions for harvestmen belonging to the suborder Laniatores. Male genitalia are important sources of taxonomic characters and are generally assumed to exhibit relatively little intraspecific variation. In contrast, descriptions of female reproductive morphology are rarely included in taxonomic descriptions of laniatorean harvestmen. As a result, relatively little is known about variation in the external features of the ovipositor. In this study, we used scanning electron microscopy to examine variation in male and female reproductive morphology among three species of harvestmen that are members of the superfamily Gonyleptoidea. Specifically, we examined the microanatomy of penises and ovipositors of Cynortula granulata (Cosmetidae), Phareicranaus calcariferus (Cranaidae), and Rhopalocranaus albilineatus (Manaosbiidae). Our results support the general observation that male reproductive morphology is conservative and displays little intraspecific variation. We observed considerable intraspecific variation in the number and shape of marginal setae on the ventral plate of the penis, but little or no variation in the morphology of the distal border of the ventral plate or the shape of the glans penis or stylus. With respect to female genitalia, we observed considerable intraspecific variation in the number of peripheral setae on the distal tip of the ovipositor. We also observed interspecific variation in the morphology of the peripheral setae (surface of the shaft and at shape of the distal tip), the distribution and morphology of smaller setae on the external surface of the ovipositor, and the surface texture of the external lobes. Our results indicate that there are several features associated with ovipositor morphology among laniatorean harvestmen that may represent potentially informative taxonomic characters. J. Morphol. 274:1415–1424, 2013.