Bernhard A. Huber

Functional Morphology of the Genitalia in the Spider Spermophora senoculata (Pholcidae, Araneae)

Abstract The reproductive biology of the spider Spermophora senoculata is investigated by microscopical observation, freeze-fixation of copulating pairs and preparation of semithin serial sections of the genitalia in functional contact. The mechanics of copulation is described in detail, revealing the functional significance of most genital structures. Before insertion, a pair of male cheliceral apophyses grasp a knob-like structure on the epigynum; the long bulbal apophyses are inserted into paired pockets on the rear of the female opisthosoma; the procursi and emboli are inserted into the uterus externus. The new data are placed in the context of data on other pholcids, and discussed with respect to morphology, function, and implications on pholcid phylogeny and sexual selection theory. The paired pockets on the female opisthosoma are interpreted to be derived from an unpaired pocket by subdivision due to space constraints. The complexity and interspecific variability of female internal genital morphology support the idea that previous models of sperm precedence patterns in spiders are overly simplistic. It is argued that grasping mechanisms may have an underestimated significance in the positioning of the genitalia. The rhythmical deformations of the female opisthosoma by the male palp agree with predictions from the hypothesis of genitalic evolution by sexual selection.

Pholcid spider molecular systematics revisited, with new insights into the biogeography and the evolution of the group

We analysed seven genetic markers sampled from 165 pholcids and 34 outgroups in order to test and improve the recently revised classification of the family. Our results are based on the largest and most comprehensive set of molecular data so far to study pholcid relationships. The data were analysed using parsimony, maximum‐likelihood and Bayesian methods for phylogenetic reconstruction. We show that in several previously problematic cases molecular and morphological data are converging towards a single hypothesis. This is also the first study that explicitly addresses the age of pholcid diversification and intends to shed light on the factors that have shaped species diversity and distributions. Results from relaxed uncorrelated lognormal clock analyses suggest that the family is much older than revealed by the fossil record alone. The first pholcids appeared and diversified in the early Mesozoic about 207 Ma ago (185–228 Ma) before the breakup of the supercontinent Pangea. Vicariance events coupled with niche conservatism seem to have played an important role in setting distributional patterns of pholcids. Finally, our data provide further support for multiple convergent shifts in microhabitat preferences in several pholcid lineages. Our findings suggest that both adaptive and non‐adaptive speciation may have played an important role in the diversification of pholcid lineages.

Phylogeny and classification of Pholcidae (Araneae): an update

Abstract For over 100 years, Eugène Simons system of pholcid classification has been used with only minor modifications. Phylogenetic research over the last decade has shown that some fundamental changes are necessary if the formal system is to reflect putative evolutionary relationships. Based on cladistic analyses of morphological and molecular data and on qualitative character assessment, the family is here divided into five subfamilies: Ninetinae, Arteminae, Modisiminae, Smeringopinae, and Pholcinae. All currently valid genera are placed in a cladogram. Even though the evidence supporting some of the nodes and assignments is weak, the cladogram generates numerous testable hypotheses and provides an improved framework for the mapping of ‘new’ characters like those from sperm ultrastructure and chromosome analysis.

ALLOMETRY OF GENITALIA AND FIGHTING STRUCTURES IN LINYPHIA TRIANGULARIS (ARANEAE, LINYPHIIDAE)

Abstract Allometric scaling is a powerful approach for studying the relationship between size, shape and function. We studied allometric slopes in Linyphia triangularis, measuring two male and one female genital characters and several male and female non-genital characters including male chelicerae that are used for fighting. As predicted from theory, genitalia had the lowest allometric values, fighting structures the highest.

The pholcid spiders of Micronesia and Polynesia (Araneae, Pholcidae)

Abstract Records of pholcid spiders from Micronesia and Polynesia are presented, along with records from Indonesia and parts of Melanesia. Nineteen species representing eleven genera are included. An illustrated key for Pacific pholcids is provided. Two species and one genus are not yet known from Micronesia or Polynesia, but are included in the key because they may occur there. Seven species are widespread synanthropic or anthropophilic species, two species are widespread native species, and nine species are endemics of one or several neighboring islands. Distribution maps include only specimens we have seen, not literature records.

Comb-hairs on the fourth tarsi in pholcid spiders (Araneae, Pholcidae)

Abstract Comb-hairs on the fourth tarsi of males and females are a classical theridioid character, but they also occur in pholcids. Previous studies on Pholcus phalangioides (Fuesslin 1775) have shown that in this species the comb-hairs function in the context of sticky silk wrap attack just as in theridiids. Here we investigate pholcid comb-hairs in a comparative way, studying the tarsal hairs of representatives of 42 pholcid genera with the SEM. We found two principal morphologies, a simple and a complex type of comb-hair. We found two principal types of comb-hair distribution on the tarsus: in distal patches or in ventral rows, but intermediate types also occur. Character mapping suggests that simple comb-hairs are derived from complex ones, and that distal patches are plesiomorphic, ventral rows derived. We speculate that pholcid comb-hairs may be derived from hairs (the “accessory claws”) that grasp silk in functional correlation with the median claw. In a female shock-frozen during wrap attack, the silk line passed through the notch of a comb-hair, but several functional details (silk grasping and releasing, function of different hair branches) remain unanswered.

EVIDENCE FOR DIRECTIONAL SELECTION ON MALE ABDOMEN SIZE IN MECOLAESTHUS LONGISSIMUS SIMON (ARANEAE, PHOLCIDAE)

Abstract Abdomens of male Mecolaesthus longissimus Simon 1893 are on average more than twice as long as in females, their length is highly variable, and they show extremely steep allometric values when scaled on body size (OLS, b = 2.64). Males cohabit with females, and they likely fight to defend this position as other pholcid spiders do. Male legs, which are usually used in pholcid male-male fights, do not show the usual high allometric values but a very low value (OLS, b = 0.37). Collectively, this lends support to the idea that M. longissimus males do not use their legs in fights and that male abdomens have assumed a role in male-male fights. However, behavioral data are missing and sexual selection by female choice or inter-male display might be involved. A large sample of data from taxonomic revisions is used to document that across pholcids, males consistently have longer tibiae 1 (and probably legs in general) than females. Several possible reasons have been suggested to account for longer male than female legs in various spider groups, but the pattern in pholcids remains to be explained.

Progress and prospects in taxonomy: what is our goal and are we ever going to reach it?

Abstract Based on percentages of undescribed species collected during intensive recent sampling campaigns in South America, tropical Africa, and the Caribbean, the current global total number of pholcid species is estimated to range from about 4,000 to 5,000. With the current rate of descriptions of about 570 pholcid species per decade, this suggests that a global inventory of the family could be completed within a few decades. However, I argue that a complete (or near-complete) inventory is neither realistic nor necessary and that knowing the majority of species of a particular group will answer most questions on that taxons biology, while being a manageable task. At current rates of description, the majority of pholcid species might be known within 10–20 years.

COLOR DIMORPHISM IN ADULTS AND JUVENILES OF BUITINGA SAFURA (ARANEAE, PHOLCIDAE)

Abstract We document the first case of a color dimorphism in a pholcid spider. Males, females and juveniles of Buitinga safura Huber 2003 either have large black spots on the abdomen or no spots, with no intermediates. At the same time, this species shows sexual dimorphism (brown prosomal marks present in males only) and continuous prosomal pattern variation in males, females and juveniles. The abdominal pigment is located in the hypodermis.

Microhabitat change drives diversification in pholcid spiders

BackgroundMicrohabitat changes are thought to be among the main drivers of diversification. However, this conclusion is mostly based on studies on vertebrates. Here, we investigate the influence of microhabitat on diversification rates in pholcid spiders (Araneae, Pholcidae). Diversification analyses were conducted in the framework of the largest molecular phylogeny of pholcid spiders to date based on three nuclear and three mitochondrial loci from 600 species representing more than 85% of the currently described pholcid genera.ResultsAssessments of ancestral microhabitat revealed frequent evolutionary change. In particular, within the largest subfamily Pholcinae, numerous changes from near-ground habitats towards leaves and back were found. In general, taxa occupying leaves and large sheltered spaces had higher diversification rates than ground-dwelling taxa. Shifts in speciation rate were found in leaf- and space-dwelling taxa.ConclusionsOur analyses result in one of the most comprehensive phylogenies available for a major spider family and provide a framework for any subsequent studies of pholcid spider biology. Diversification analyses strongly suggest that microhabitat is an important factor influencing diversification patterns in pholcid spiders.