Viruses encoding a replication-associated protein (Rep) within a covalently closed, single-stranded (ss)DNA genome are among the smallest viruses known to infect eukaryotic organisms, including economically valuable agricultural crops and livestock. Although circular Rep-encoding ssDNA (CRESS DNA) viruses are a widespread group for which our knowledge is rapidly expanding, biased sampling toward vertebrates and land plants has limited our understanding of their diversity and evolution. Here, we screened terrestrial arthropods for CRESS DNA viruses and report the identification of 44 viral genomes and replicons associated with specimens representing all three major terrestrial arthropod lineages, namely Euchelicerata (spiders), Hexapoda (insects), and Myriapoda (millipedes). We identified virus genomes belonging to three established CRESS DNA viral families (Circoviridae, Genomoviridae, and Smacoviridae); however, over half of the arthropod-associated viral genomes are only distantly related to currently classified CRESS DNA viral sequences. Although members of viral and satellite families known to infect plants (Geminiviridae, Nanoviridae, Alphasatellitidae) were not identified in this study, these plant-infecting CRESS DNA viruses and replicons are transmitted by hemipterans. Therefore, members from six out of the seven established CRESS DNA viral families circulate among arthropods. Furthermore, a phylogenetic analysis of Reps, including endogenous viral sequences, reported to date from a wide array of organisms revealed that most of the known CRESS DNA viral diversity circulates among invertebrates. Our results highlight the vast and unexplored diversity of CRESS DNA viruses among invertebrates and parallel findings from RNA viral discovery efforts in undersampled taxa.

In 1978, Oster and Wilson proposed a bang-bang investment strategy for social insects in which colony size at maturity amplifies colony reproduction. In this paper, the investment strategies of the monogyne form of the fire ant, Solenopsis invicta, were compared to the predictions of the bang-bang model. Demographic census data, collected on fire ant mounds excavated every month during the years 1985 and 1988, revealed that colony reproduction was independent of colony size (~50,000 to ~250,000 workers). Why were mature S. invicta colonies up to five times larger than they needed to be to reproduce an annual batch of sexual offspring? To address this question, Oster and Wilson's bang-bang model was modified to a "yoyo-bang" investment strategy for perennial societies. In the yoyo-bang model, excess workers are a disposable reserve - a buffer - that can oscillate up or down depending on resource availability without adversely affecting annual reproductive cycles. The yoyo-bang model links colony size, colony survival and lifetime reproductive fitness.

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Colonies of the monogyne social form of the red imported fire ant, Solenopsis invicta, may contain half a million workers per nest. Spatially organizing such a large group within the confines of a single nest requires a pragmatic architectural design. The morphology of field mounds and subterranean nest chambers of S. invicta were determined using several cast methods. The above-ground portion of a fire ant nest, the mound, consisted of a dense matrix of narrow tunnels. Below ground level, subterranean shafts and nodes were excavated through the grass root system (10 -20 cm), connecting the mound tunnels to the subterranean chambers. Chambers averaged ~5 cm 2 and appeared at depths from 10 -80 cm below ground level. The orientation of mound tunnels and subterranean shafts was more often vertical than horizontal, probably facilitating the diurnal micro-migration of colony members back and forth from the subterranean chambers to the mound. The mean size of groups in the subterranean chambers of field nests was remarkably small relative to colony size (~200 individuals per chamber: 50% workers, 50% brood). In laboratory experiments, neither crowding nor nest partitioning affected brood rearing. The possibility that small group size and nest complexity generate localized or time-released communication signals is discussed.

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