Research

Inbreeding: Genetic diversity is the basis of evolutionary potential of species to respond to environmental change and disease. Due to habitat fragmentation and disappearing strains and breeds for human food production, the long term consequences of inbreeding on the evolutionary persistence of lineages is a rapidly growing concern for conservation and livestock genetics. The social spiders offer a unique opportunity to study the effects of inbreeding, as sociality in spiders is accompanied by a switch to inbreeding. Inbreeding and consequent low genetic variability may be the primary cause of the apparent long-term failure of sociality. Recently, in collaboration with Drs Wayne Maddison and Leticia Avilés, my research has begun to focus on the long term consequences of inbreeding on the genetic variability and evolvability of lineages (Agnarsson et al. 2009). Broadly I'm interested in studying traits that incur conflict in time scales, or levels of selection; traits (e.g. asexuality) beneficial for individuals or groups in the short term but that may lead to long term failure of the trait-bearing lineage.

Cetacean phylogenetics and evolution of acoustic communication: Cetacea-whales, porpoises, and dolphins-is one of the most intensely studied groups of organisms on earth. Among the most intriguing aspects of cetacean biology is their complexity of communication though acoustic signals. While interest in the phylogenetic position of cetaceans, and the interrelationship of their major lineages (e.g. toothed whales and baleen whales) is intense, the lower level phylogenetics (relationships among species) have lagged behind. Perhaps consequently, while hypotheses about the evolution of cetacean acoustic communication abound, they remain effectively 'phylogeny-independent', hence in a very real sense untested. In collaboration with Laura May-Collado we have provided the most detailed species-level phylogeny of Cetacea to date (May-Collado and Agnarsson 2006), and are using it to test some of the prominent hypotheses on the evolution of acoustics (May-Collado et al. 2007a, b).

Morphology and homology: My work on morphology mostly serves to gather character data for phylogenetics (Agnarsson 2003c, 2004, 2005, 2006a; Agnarsson & Kuntner 2005). As such I am interested in the theoretical problem of proposing and testing homology hypotheses. In collaboration with Jonathan Coddington we have developed the first quantitative method to test character homology, a step towards reducing the subjectivity of character coding (Agnarsson and Coddington 2008).

Theridiidae: The family Theridiidae is one of the largest spider families and well known for their ecological, morphological, and behavioral diversity. However, prior to the work of my collaborators and I, no phylogeny existed preventing the testing of a myriad of hypothesis on the evolution of various traits and behaviors. To date,we have proposed cladistic hypotheses for about half of the theridiid genera (Agnarsson 2003c, 2004, 2005, 2006a, b, c; Agnarsson and Kuntner 2005; Avilés et al. 2006, Arnedo et al. 2004, 2007). These phylogenies offer the essential backbone for hypothesis testing in the diverse fields these spiders serve as exemplar study organisms. To date, we have proposed cladistic hypotheses for 35 theridiid genera based on

morphology (Agnarsson 2003c, 2004, 2006) and over 40 genera based on molecular data (Arnedo et al. 2004, 2007), with an overlap of 32 genera between the two datasets. These phyologenies thus represent nearly half of the theridiid genera and all the subfamilies.

Anelosimus: About a third of all social spiders-eight species-belong to the theridiid genus Anelosimus whose species therefore have become model organisms in the

study of spider sociality. I have revised all the New World Anelosimus species, in addition to species from Madagascar (Agnarsson and Kuntner 2005), and mainland Africa and Southeast Asia (Agnarsson and Zhang 2006), and proposed a phylogenetic hypothesis using world-wide exemplars (Agnarsson 2005, 2006b; Agnarsson et al. 2007). Current work focuses on broadening the taxon sampling for species level phylogenies, and on the effect of sociality and inbreeding on genetic diversity and structure (Agnarsson et al. 2009).

Research

Sociality: The evolution of social behavior has been of great interest to biologists since Darwin first addressed this "one special difficulty". Since Darwin the study of sociality has itself evolved to become a sub-discipline of biology: sociobiology. Sociality continues to excite. It represents a conflict between individual and group benefits, and eusociality perplexes as a strategy entailing ecological dominance, yet one that rarely evolves. The evolution of sociality from non-social ancestors is still poorly understood and in that respect spiders are an excellent study group for sociobiologists. They represent the largest clade of exclusively predatory animals and are famously solitary and aggressive, even towards their own offspring and potential mating partners. To become social they thus have to overcome hindrances (aggressiveness, cannibalism) that most other social organism never faced. Furthermore, they lack the most frequently cited correlate of sociality, namely haplodiploidy. Hence factors that may facilitate sociality in spiders are quite possibly important in other social organisms. My research focuses on testing hypotheses of social preadaptations and consequences of sociality in a phylogenetic framework. Strikingly my phylogenetic results (Agnarsson 2005, 2006; Agnarsson et al. 2007) imply that almost every social spider evolved sociality independently. The frequent evolution and spindly distribution of social spiders suggests a conflict in evolutionary time scale. Sociality seems to afford short term benefits, but have negative long term consequences; lack of diversification suggest spider sociality is effectively an evolutionary dead-end (Agnarsson et al. 2006). For further detail and a list of the social spiders.

Tropical Biodiversity: Scientifically-based responses to the current extinction crisis require that tropical field biologists rapidly gather and synthesize basic information on the structure and distribution of tropical biodiversity at a number of spatial and evolutionary scales. In collaboration with Jonathan Coddington and others I am involved in work on biodiversity inventories in the tropics and on inventory theory and design (Coddington et al. 2009). A major theoretical issue is explaining rarity-the high percentage of sampled species in typical biodiversity inventories represented by only a single individuals-essentially as undersampling bias, and indicator of survey completeness.

Intertidal organisms, zonation and dispersal: Our understanding of animal communities in the intertidal stems nearly entirely from research done during low tide, when the shore is accessible, but when many animals are relatively inactive. In collaboration with Agnar Ingólfsson at the University of Iceland we study the intertidal during high tide, in rocky shores in Iceland. Our research (Ingólfsson & Agnarsson 1999, 2003) demonstrates that zonation patterns change at high tide (species move) and that important species had hitherto been entirely overlooked. In particular the voracious amphipod Anonyx sarsi is absent in the intertidal during low tide, but abundant and likely a dominant predator and scavenger in the intertidal during high tide. A more complete understanding of the intertidal community will require further studies, unconstrained by the convenience of low tide.

Kleptoparasitism: Spider kleptoparasites occupy heterospecific spider webs to steal resources. From the perspective of obligatory klepto-parasites, host webs are natural habitat patches, or islands. I am interested in the distribution of kleptoparasites among host webs, and the potential of this study system for ecological research. A clear correlation exists between patch (web) size and kleptoparasite load and population stability increases with patch connectivity (Agnarsson 2003). These characteristics epitomize general ecological models, such as island biogeography and metapopulation biology and this study system lends itself to their testing and development. Another aspect of kleptoparasitism is that like in sociality, gregariousness entails tolerance. At some level tolerance displayed in the two behaviors may be homologous (Agnarsson 2002, Whitehouse et al. 2002), i.e. that behaviors that facilitated the evolution of sociality (such as maternal care) could also have facilitated kleptoparasitism.
Theridiidae Webs: Spider webs are extraordinary examples of animal architecture. Orb webs are the most famous, and best studied web types. They are remarkably conserved through evolutionary time and web characteristics provide many reliable characters for phylogenetic reconstruction. The derived orb-web weavers Theridiidae, that no longer make orb webs, however, are marked by an extraordinary diversity in web design, plasticity and frequent convergence (Eberhard et al. 2008). We speculate that their diversity is a result of relaxed stereotypy, introducing variation that in turn can lead to the emergence of various new web forms.

Icelandic arachnids: My first steps in Arachnology were two detailed synopses of Icelandic arachnids (Agnarsson 1996, 1998). As a result of this work, these previously largely ignored groups are now among the few routinely identified in sampling-based ecological research in Iceland.

Spider silk biomechanics: Spiders produce silks that have remarkable physical properties, such as absorbing more energy before breaking than any other biological and most manmade materials. Spider silk is therefore a high priority for biotechnological exploitation and development for human use. The Araneidae is the most diverse family of orb web-building (wheel-shaped webs) spiders, exhibiting a variety of ecological specializations that are not found in other families. Orbwebs function as traps for flying insects through a combination of properties from two types of fibers – stiff supporting threads and stretchy capture spirals. My work in collaboration with T. Blackledge et al. uses molecular phylogenies to analyze the evolutionary history of the material properties of the two primary constituent fibers of orbwebs, frame threads and sticky capture silks, across ecologically diverse and phylogenetically broad set of araneids (Agnarsson et al. 2008; Agnarsson et al. 2009a, b; Blackledge et al. 2009).

My current research interests span a range of topics, including (in no particular order) morphology, taxonomy, biodiversity estimation, sociality, inbreeding, phylogenetics, silk biomechanics, acoustic communication, biogeography, phylogeography, and phylogenetic theory. My main research applies phylogenetics, and population genetics, to address evolutionary questions in organisms as unlike as arthropods and whales, using data derived from morphology, behavior, and DNA.

Phylogeny of Mammals: Few, if any, groups of organisms on earth are better studied than mammals. Yet, despite their high profile detailed species-level phylogenies are lacking for most mammalian orders. Our work focuses on providing taxon-rich phylogenies of mammal orders as tools for comparative biology. Groups we have worked on so far include Cetacea (May-Collado and Agnarsson 2006), Cetartiodactyla (Agnarsson and May-Collado 2008), Carnivora (Agnarsson et al. in review), and Rodentia (Sobrero et al. in review)