The ecology of sex explains patterns of helping in arthropod societies

Authors thank the Natural Sciences and Engineering Research Council of Canada (NGD), the Clarendon Fund (NGD) and the Natural Environment Research Council (LR, NE/K009516/1; AG, NE/K009524/1) for funding.Across arthropod societies, sib-rearing (e.g. nursing or nest defence) may be provided by females, by males or by both sexes. According to Hamilton's ‘haplodiploidy hypothesis’, this diversity reflects the relatedness consequences of diploid vs. haplodiploid inheritance. However, an alternative ‘preadaptation hypothesis’ instead emphasises an interplay of ecology and the co-option of ancestral, sexually dimorphic traits for sib-rearing. The preadaptation hypothesis has recently received empirical support, but remains to be formalised. Here, we mathematically model the coevolution of sex-specific helping and sex allocation, contrasting these hypotheses. We find that ploidy per se has little effect. Rather, the ecology of sex shapes patterns of helping: sex-specific preadaptation strongly influences who helps; a freely adjustable sex ratio magnifies sex biases and promotes helping; and sib-mating, promiscuity, and reproductive autonomy also modulate the sex and abundance of helpers. An empirical survey reveals that patterns of sex-specific helping in arthropod taxa are consistent with the preadaptation hypothesis.Publisher PDFPeer reviewe

Characteristics of the nuclear (18S, 5.8S, 28S and 5S) and mitochondrial (12S and 16S) rRNA genes of Apis mellifera (Insecta: Hymenoptera): structure, organization, and retrotransposable elements

As an accompanying manuscript to the release of the honey bee genome, we report the entire sequence of the nuclear (18S, 5.8S, 28S and 5S) and mitochondrial (12S and 16S) ribosomal RNA (rRNA)-encoding gene sequences (rDNA) and related internally and externally transcribed spacer regions of Apis mellifera (Insecta: Hymenoptera: Apocrita). Additionally, we predict secondary structures for the mature rRNA molecules based on comparative sequence analyses with other arthropod taxa and reference to recently published crystal structures of the ribosome. In general, the structures of honey bee rRNAs are in agreement with previously predicted rRNA models from other arthropods in core regions of the rRNA, with little additional expansion in non-conserved regions. Our multiple sequence alignments are made available on several public databases and provide a preliminary establishment of a global structural model of all rRNAs from the insects. Additionally, we provide conserved stretches of sequences flanking the rDNA cistrons that comprise the externally transcribed spacer regions (ETS) and part of the intergenic spacer region (IGS), including several repetitive motifs. Finally, we report the occurrence of retrotransposition in the nuclear large subunit rDNA, as R2 elements are present in the usual insertion points found in other arthropods. Interestingly, functional R1 elements usually present in the genomes of insects were not detected in the honey bee rRNA genes. The reverse transcriptase products of the R2 elements are deduced from their putative open reading frames and structurally aligned with those from another hymenopteran insect, the jewel wasp Nasonia (Pteromalidae). Stretches of conserved amino acids shared between Apis and Nasonia are illustrated and serve as potential sites for primer design, as target amplicons within these R2 elements may serve as novel phylogenetic markers for Hymenoptera. Given the impending completion of the sequencing of the Nasonia genome, we expect our report eventually to shed light on the evolution of the hymenopteran genome within higher insects, particularly regarding the relative maintenance of conserved rDNA genes, related variable spacer regions and retrotransposable elements

Nitrogen, phosphorus, and liming effects of poultry layer manures in coastal plain and Piedmont soils

Since soil type and manure processing can affect nutrient release, laboratory and greenhouse experiments determined N and P availability, and liming value under representative layer manure application scenarios. Fresh, composted, and pelleted manures were applied to surface samples of three North Carolina soils (Belhaven, loamy, mixed, dysic, thermic Terric Haplosaprists; Cecil, fine, kaolinitic, thermic Typic Kanhapludults; and Lynchburg, fine-loamy, siliceous, semiactive, thermic Aeric Paleaquults). A 90 d N mineralization incubation found greater N mineralization (83, 73, and 61% of total N applied in fresh, composted, and pelleted manures, respectively), in the Lynchburg than in the Cecil soil (41, 33, and 25% for the same manures); while mean N availability of urea was 80% for all soils. All manures exhibited effects on soil pH and Mehlich-3 extractable soil P during separate 21 d incubations that were consistent with their calcium carbonate equivalence and total P content. In a 30 d greenhouse experiment with millet [Urochloa ramosa (L.) T. Q. Nguyen] in the same soils, plant available N from the manures followed the decreasing order of fresh > composted > pelleted, similar to the rank order obtained in the N incubation study. Application of either inorganic or manure P sources to the Belhaven muck resulted in more water soluble soil P and greater plant P uptake than when P was applied to the mineral soils. Both soil and manure source influenced manure nutrient availability, but the availability coefficients from these laboratory and greenhouse experiments should be verified under field conditions.D. F. Montalvo Grijalva, C. R. Crozier, T. J. Smyth, and D. H. Hard