Generalized centrality in trees

In 1982, Slater defined path subgraph analogues to the center, median, and (branch or branchweight) centroid of a tree. We define three families of central substructures of trees, including three types of central subtrees of degree at most D that yield the center, median, and centroid for D = 0 and Slater's path analogues for D = 2. We generalize these results concerning paths and include proofs that each type of generalized center and generalized centroid is unique. We also present algorithms for finding one or all generalized central substructures of each type.

A review of the Nearctic jumping spiders (Araneae: Salticidae) of the subfamily Euophryinae north of Mexico

The generic and specific composition ofthe Nearctic jumping spiders ofthe subfamily Euophryinae north of Mexico is reviewed, and the biogeographic affinities of the constituent groups are diagnosed. The five North American species of HabrocestUln are removed from that non-euophryine genus; four are placed in the New Genus Naphrys, type species Habrocestum acerbum Peckham & Peckham 1909, creating the following New Combinations: Naphrys acerba (Peckham & Peckham), Naphrys bufoides (Chamberlin & Ivie 1944), Naphrys pulex (Hentz 1846), and Naphrys xerophila (Richman 1981). The fifth species is not an euophryine, and becomes Chinattus parvulus (Banks 1895), New Combination. Four species placed in the genus Tylogonus, another non-euophryine genus, are removed to the New Genus Mexigonus, type species Sidusa minuta F.O.P.-Cambridge 1901, creating the following New Combinations: Mexigonus arizonensis (Banks 1904), Mexigonus dentichelis (F.O.P.-Cambridge 1901),Mexigonus minutus (F.O.P.-Cambridge), and Mexigonus morosus (Peckham & Peckham 1888). One of the two species of Nearctic Euophrys has been misplaced, and becomes Chalcoscirtus diminutus (Banks 1896), New Combination. New state records are reported for Chalcoscirtus diminutus [Kansas, Michigan, Minnesota, Missouri, Nebraska, New Mexico], Mexigonus minutus [California], Naphrys acerba [New Mexico], and Pseudeuophrys erratica (Walckenaer 1826) [New York]. Of the eight known euophryine genera with Nearctic representatives, Anasaitis (one species) and Cory thalia (two species) are considered Neotropical in origin, whereas Chalcoscirtus (three species), Ezwphrys (one species), and Talavera (one species) are considered Holarctic. The Palaearctic Pseudeuophrys erratica is introduced. The affinities of the apparently endemic Nearctic Naphrys (four species) and Mexigonus (four species) are uncertain at this time. Although not an euophryine, the presence of a species of Chinattus in eastern North America is biogeographically interesting, as the other species in the genus are Asian; it joins a diversity of taxa with this distribution

Nest-Site Selection by Female Black-Capped Chickadees: Settlement Based on Conspecific Attraction?

Female Black-capped Chickadees (Poecile atricapillus) solicit extrapair copulations (EPCs) from neighboring high-ranking males, and these EPCs result in extrapair young. Females might choose to locate their nests near the territory boundaries of attractive males to facilitate access to EPCs. Other hypotheses might also explain choice of nest site, namely (1) habitat characteristics, (2) prey abundance, and (3) previous experience. We tested these four hypotheses in 1996 and 1997. Out of 27 habitat characteristics measured, we found only one that was significantly different between nests and control sites in both years. The abundance of large trees was lower at nest sites than at control sites in each year and when years were pooled. Relative prey abundance did not differ between nests and control sites for either year of the study. We found no different in interyear nest placement based on female experience; experienced females nester farther than 60 m from their previous nest sites in both years of the study. In 1996, females whose neighboring males were higher ranked than their social partner located their nests significantly closer to territory boundaries than did females whose nearest neighbors were lower ranked than their social partner. In 1997, all pairs nested near territory boundaries. We conclude that choice of nest location in Black-capped Chickadees is influenced by conspecific attraction based on mating tactics

Dramatic expansion of the black widow toxin arsenal uncovered by multi-tissue transcriptomics and venom proteomics.

BackgroundAnimal venoms attract enormous interest given their potential for pharmacological discovery and understanding the evolution of natural chemistries. Next-generation transcriptomics and proteomics provide unparalleled, but underexploited, capabilities for venom characterization. We combined multi-tissue RNA-Seq with mass spectrometry and bioinformatic analyses to determine venom gland specific transcripts and venom proteins from the Western black widow spider (Latrodectus hesperus) and investigated their evolution.ResultsWe estimated expression of 97,217 L. hesperus transcripts in venom glands relative to silk and cephalothorax tissues. We identified 695 venom gland specific transcripts (VSTs), many of which BLAST and GO term analyses indicate may function as toxins or their delivery agents. ~38% of VSTs had BLAST hits, including latrotoxins, inhibitor cystine knot toxins, CRISPs, hyaluronidases, chitinase, and proteases, and 59% of VSTs had predicted protein domains. Latrotoxins are venom toxins that cause massive neurotransmitter release from vertebrate or invertebrate neurons. We discovered ≥ 20 divergent latrotoxin paralogs expressed in L. hesperus venom glands, significantly increasing this biomedically important family. Mass spectrometry of L. hesperus venom identified 49 proteins from VSTs, 24 of which BLAST to toxins. Phylogenetic analyses showed venom gland specific gene family expansions and shifts in tissue expression.ConclusionsQuantitative expression analyses comparing multiple tissues are necessary to identify venom gland specific transcripts. We present a black widow venom specific exome that uncovers a trove of diverse toxins and associated proteins, suggesting a dynamic evolutionary history. This justifies a reevaluation of the functional activities of black widow venom in light of its emerging complexity

Intragenic homogenization and multiple copies of prey-wrapping silk genes in Argiope garden spiders.

BackgroundSpider silks are spectacular examples of phenotypic diversity arising from adaptive molecular evolution. An individual spider can produce an array of specialized silks, with the majority of constituent silk proteins encoded by members of the spidroin gene family. Spidroins are dominated by tandem repeats flanked by short, non-repetitive N- and C-terminal coding regions. The remarkable mechanical properties of spider silks have been largely attributed to the repeat sequences. However, the molecular evolutionary processes acting on spidroin terminal and repetitive regions remain unclear due to a paucity of complete gene sequences and sampling of genetic variation among individuals. To better understand spider silk evolution, we characterize a complete aciniform spidroin gene from an Argiope orb-weaving spider and survey aciniform gene fragments from congeneric individuals.ResultsWe present the complete aciniform spidroin (AcSp1) gene from the silver garden spider Argiope argentata (Aar_AcSp1), and document multiple AcSp1 loci in individual genomes of A. argentata and the congeneric A. trifasciata and A. aurantia. We find that Aar_AcSp1 repeats have >98% pairwise nucleotide identity. By comparing AcSp1 repeat amino acid sequences between Argiope species and with other genera, we identify regions of conservation over vast amounts of evolutionary time. Through a PCR survey of individual A. argentata, A. trifasciata, and A. aurantia genomes, we ascertain that AcSp1 repeats show limited variation between species whereas terminal regions are more divergent. We also find that average dN/dS across codons in the N-terminal, repetitive, and C-terminal encoding regions indicate purifying selection that is strongest in the N-terminal region.ConclusionsUsing the complete A. argentata AcSp1 gene and spidroin genetic variation between individuals, this study clarifies some of the molecular evolutionary processes underlying the spectacular mechanical attributes of aciniform silk. It is likely that intragenic concerted evolution and functional constraints on A. argentata AcSp1 repeats result in extreme repeat homogeneity. The maintenance of multiple AcSp1 encoding loci in Argiope genomes supports the hypothesis that Argiope spiders require rapid and efficient protein production to support their prolific use of aciniform silk for prey-wrapping and web-decorating. In addition, multiple gene copies may represent the early stages of spidroin diversification

The Victorian Naturalist

v.114 (1997

Further faunistic notes on Cozyptila and Xysticus from Turkey (Aranea, Thomisidae)

Nine recently described or poorly known species of the thomisid genera Cozyptila Lehtinen & Marusik, 2005 and Xysticus C.L. Koch, 1835 are reported from Turkey. Five species, Cozyptila blackwalli (Simon, 1875), C. thaleri Marusik & Kovblyuk, 2005, Xysticus bacurianensis Mcheidze, 1971, X. thessalicoides Wunderlich, 1995 and X. xerodermus Strand, 1913, are new records for the Turkish spider fauna. Two species, X. bacurianensis and X. xerodermus are illustrated and a distribution map is provided for the former. A few additional records are given for Greece and the Caucasian countries, of which X. bacurianensis is new for Azerbaijan

New Integrality Gap Results for the Firefighters Problem on Trees

The firefighter problem is NP-hard and admits a $(1-1/e)$ approximation based on rounding the canonical LP. In this paper, we first show a matching integrality gap of $(1-1/e+\epsilon)$ on the canonical LP. This result relies on a powerful combinatorial gadget that can be used to prove integrality gap results for many problem settings. We also consider the canonical LP augmented with simple additional constraints (as suggested by Hartke). We provide several evidences that these constraints improve the integrality gap of the canonical LP: (i) Extreme points of the new LP are integral for some known tractable instances and (ii) A natural family of instances that are bad for the canonical LP admits an improved approximation algorithm via the new LP. We conclude by presenting a $5/6$ integrality gap instance for the new LP.Comment: 22 page