John W. Wenzel

Reconstructing web evolution and spider diversification in the molecular era

The evolutionary diversification of spiders is attributed to spectacular innovations in silk. Spiders are unique in synthesizing many different kinds of silk, and using silk for a variety of ecological functions throughout their lives, particularly to make prey-catching webs. Here, we construct a broad higher-level phylogeny of spiders combining molecular data with traditional morphological and behavioral characters. We use this phylogeny to test the hypothesis that the spider orb web evolved only once. We then examine spider diversification in relation to different web architectures and silk use. We find strong support for a single origin of orb webs, implying a major shift in the spinning of capture silk and repeated loss or transformation of orb webs. We show that abandonment of costly cribellate capture silk correlates with the 2 major diversification events in spiders (1). Replacement of cribellate silk by aqueous silk glue may explain the greater diversity of modern orb-weaving spiders (Araneoidea) compared with cribellate orb-weaving spiders (Deinopoidea) (2). Within the “RTA clade,” which is the sister group to orb-weaving spiders and contains half of all spider diversity, >90% of species richness is associated with repeated loss of cribellate silk and abandonment of prey capture webs. Accompanying cribellum loss in both groups is a release from substrate-constrained webs, whether by aerially suspended webs, or by abandoning webs altogether. These behavioral shifts in silk and web production by spiders thus likely played a key role in the dramatic evolutionary success and ecological dominance of spiders as predators of insects.

The origin of photic behavior and the evolution of sexual communication in fireflies (Coleoptera: Lampyridae)

Through a phylogenetic analysis using adult morphological characters, we show that the origin of bioluminescence in cantharoid beetles appears to predate the origin of the family Lampyridae. The ability to produce and emit photic signals was first gained by larvae and appears to function as an aposematic warning display; it was subsequently gained in adults and is used as a sexual signal. Our analysis also suggests that while pheromonal sexual signals are used basally in the family, they are used in conjunction with and then subsequently replaced by photic signals in some lampyrid lineages. Both photic signals and the photic organs used to produce them have become greatly elaborated in the fireflies that no longer employ pheromonal sexual signals. In addition, the ability to produce a flashed sexual signal appears to have arisen at least three times in the family Lampyridae. Convergent evolution is also evident in a number of adult male photic organ morphologies. Further, we recommend that individual signal system components be compared rather than overall signal system complexity. The use of this strategy may allow one to recognize and better interpret adaptive correlations despite convergence or loss. We demonstrate that phylogenetic analysis is a powerful tool even for rapidly evolving traits.

SILK MEDIATED DEFENSE BY AN ORB WEB SPIDER AGAINST PREDATORY MUD-DAUBER WASPS

Stabilimenta are zigzag and spiral designs of seemingly conspicuous silk included at the centers of many spider webs. We examined the association of stabilimenta with the ability of spiders to defend themselves against predatory mud-dauber wasps. We found that Argiope trifasciata (Araneae, Araneidae) were significantly more likely to survive attacks by Chalybion caeruleum and Sceliphron caementarium (Hymenoptera, Sphecidae) when spiders included stabilimenta in webs. This association could not be explained by factors such as differences in sizes or conditions of spiders nor locations of webs. We suggest that stabilimenta may function to delay pursuit of spiders as they drop from webs by physically blocking wasps, camouflaging spiders or distracting attacking wasps. Stabilimenta may function in a role very similar to the retreats built by many other genera of spiders and appear to be an adaptation to reduce the predation pressure faced by spiders that have evolved foraging habits at highly exposed diurnal web sites.

Evolution of Caste in Neotropical Swarm-Founding Wasps(Hymenoptera: Vespidae; Epiponini)

Abstract Reproductive castes are compared in species of swarming wasps representing all currently recognized genera of Epiponini (Polistinae). New morphometric data for nine measures of body parts and ovarian data are presented for 13 species. These are integrated with all similarly conducted available studies, giving a total of 30 species. Analysis reveals several syndromes relating reproductive and nonreproductive individuals: no meaningful distinction, physiological differences only, reproductives larger than nonreproductives with intermediate individuals present, reproductives different in shape from nonreproductives with no intermediates, and reproductives smaller in some aspects than nonreproductives. Distribution of these syndromes among species is consistent with phylogenetic relationships derived from other data. Optimizing these syndromes on the cladogram indicates that the basal condition of Epiponini is a casteless society that is not comparable to the primitively social genus Polistes where dominant queens control reproduction. Castes originate several times in Epiponini, with different results in different lineages. The best documented evolutionary sequence passes from casteless societies, to those with reproductives larger, to those with reproductives differing in shape from nonreproductives, to those with reproductives smaller in some measures. This sequence is consistent with Wheelers theory of the origin of caste through developmental switches, and represents the most thorough test of that theory to date.

THE EVOLUTION OF BIOLUMINESCENCE IN CANTHAROIDS (COLEOPTERA: ELATEROIDEA)

We present the first cladistic analysis of genera in the family Lampyridae and other closely related beetles. A monophyletic concept of Lampyridae is established. The phylogenetic positions of the luminous cantharoid families [Omalisidae, Rhagophthalmidae and Phengodidae] in relation to Lampyridae are discussed, as well as the implications of the evolution of bioluminescence and photic signaling in this group of beetles. The Rhagophthalmidae appears to include Dioptoma and Diplocladon (formerly located in Phengodidae) and the Phengodidae apparently includes Stenocladius (formerly of Lampyridae). Harmatelia, Drilaster and Pterotus are transferred to Elateroidea insertae sedis and not included in Lampyridae where they were sometimes placed.

Organization and Regulation of Nest Construction Behavior in Metapolybia Wasps

Field observations and experiments revealed that construction behavior of Metapolybia wasps is based on parallel processing and distributed decision making. Sixteen behaviors were used to separate five behavioral groupings: specialized water forager, flexible pulpforager, active builder, active generalist, and idle. The idle category proved to be the source and the sink of the other task groups, although specialist foragers tend to retain their duties or take over other active roles. Nest construction is partitioned into three tasks. Pulp foragers transfer wood-pulp to the nest where other wasps (builders) distribute and process it further. The builders incorporate this material into the nest structure on the basis of individual decisions. Water foragers provide the extra water necessary for both building and pulp collecting. Material exchange takes place on the nest between pairs or in small groups. The duration and frequency of different behaviors, the number of wasps belonging to different behavioral groups, and the different scale of specialization in different groups suggest that the colony-level performance and speed are governed by the activity of the pulp foragers, who receive information about both the water saturation level of the colony and the activity of the builders through local interactions. Several predictions of this hypothesis were supported by disturbing the normal construction behavior through removing or decreasing the number of individuals belonging to different behavioral groups or supplying additional building material.

From basepairs to birdsongs: phylogenetic data in the age of genomics

Given the quantity of molecular data now available, including complete genomes for some organisms, one can ask whether there is a need for any data beyond complete genomic sequences for phylogenetic analysis. One reason to look beyond the genome is that not all character information is encoded in organismal genomes. We propose a hierarchy of characters that ranges from biologically transmitted but nongenomically encoded characters, such as bird songs, to characters that are genomically encoded. All of these characters can retain historical information and are potentially useful for phylogenetic analysis. In addition, a number of phenotypic levels that are expressions of the genome can be identified. The question whether it is worth including any of these levels if all of the underlying sequence data have been collected arises, since issues of redundancy occur. Utilization of phenotypic levels that are ultimately based on sequences may facilitate reconstructing homologies that are not evident from sequence data alone. We propose the use of simultaneous analysis of sequence data and as many levels of phenotypic characters as possible to take advantage of homology information that may be more easily recovered from the latter. A method that eliminates redundancy to the degree that it can be detected is proposed.

Phylogeny of bird‐grasshopper subfamily Cyrtacanthacridinae (Orthoptera: Acrididae) and the evolution of locust phase polyphenism

Locust phase polyphenism is an extreme form of density‐dependent phenotypic plasticity in which solitary and cryptic grasshoppers can transform into gregarious and conspicuous locusts in response to an increase in local population density. We investigated the evolution of this complex phenotypic plasticity in a phylogenetic framework using a morphological phylogeny of Cyrtacanthacridinae, which contains some of the most important locust species, and a comprehensive literature review on the biology and ecology of all known members of the subfamily. A phylogenetic analysis based on 71 morphological characters yielded a well‐resolved tree and found that locust phase polyphenism evolved multiple times within the subfamily. The literature review demonstrated that many cyrtacanthacridine species, both locust and sedentary, are capable of expressing density‐dependent color plasticity. When this color plasticity was divided into two smaller components, background coloration and development of black pigmentation, and when these plastic traits were optimized on to the phylogeny, we found that the physiological mechanisms underlying this plasticity were plesiomorphic for the subfamily. We also found that different locust species in Cyrtacanthacridinae express both similarities and differences in their locust phase polyphenism. Because locust phase polyphenism is a complex syndrome consisting of numerous plastic traits, we treat it as a composite character and dissected it into smaller components. The similarities among locust species could be attributed to shared ancestry and the differences could be attributed to the certain components of locust phase polyphenism evolving at different rates.

Revision and Cladistic Analysis of the Nocturnal Social Wasp Genus, Apoica Lepeletier (Hymenoptera: Vespidae; Polistinae, Epiponini)

Abstract A revision of the nocturnal social wasp genus, Apoica, is presented. The revision is based on a cladistic analysis of morphological, behavioral, and molecular characters of the nine nominal species. The subgenera Deuterapoica and Apoica are consistent with the phylogenetic results, and are thus retained. A new species, Apoica ellenae, whose phylogenetic position is uncertain, is described. A variant of A. albimacula from Peru is noted. This brings the total number of species in the genus to 10.

Larval case architecture and implications of host-plant associations for North American Coleophora (Lepidoptera; Coleophoridae)

The case-bearing moths of North America are represented by a single genus, Coleophora, which contains approximately 144 described species. All are external seed or leaf miners that inhabit portable silk cases during most of the larval stage. Architectural and ecological characters from larval cases were used in cladistic analysis to investigate existing case groups for 32 North American species of Coleophora. Cladistic analysis confirmed monophyly of certain case groups, but not of others. Host-plant preferences were also examined. The pattern of host plant use reflects more closely preference for certain plant tissues (seeds versus leaves) and growth forms (herbaceous versus woody) with exploitation of different plant taxa, rather than preference for certain plant taxa with exploitation of different plant tissues. q 2002 The Willi Hennig