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Phenotypic traits are often integrated into evolutionary modules: sets of organismal parts that evolve together. In social insect colonies, the concepts of integration and modularity apply to sets of traits both within and among functionally and phenotypically differentiated castes. On macroevolutionary timescales, patterns of integration and modularity within and across castes can be clues to the selective and ecological factors shaping their evolution and diversification. We develop a set of hypotheses describing contrasting patterns of worker integration and apply this framework in a broad (246 species) comparative analysis of major and minor worker evolution in the hyperdiverse ant genus Pheidole. Using geometric morphometrics in a phylogenetic framework, we inferred fast and tightly integrated evolution of mesosoma shape between major and minor workers, but slower and more independent evolution of head shape between the two worker castes. Thus, Pheidole workers are evolving as a mixture of intracaste and intercaste integration and rate heterogeneity. The decoupling of homologous traits across worker castes may represent an important process facilitating the rise of social complexity. [ABSTRACT FROM AUTHOR]

Study of extreme phenotypic traits and novel structures provides insights into forces mediating evolution and diversification. Sexual selection is often implicated as the evolutionary driver of trait exaggeration, while examples invoking natural selection are scarce. Heretofore overlooked examples include outlandishly exaggerated spines produced by the non-reproductive castes of various ant lineages. Ant spines are conjectured to be defensive weapons, but factors shaping their evolution are poorly understood. Here we assess the evolution, ecology and biomechanics of spine exaggeration in the hyperdiverse genus Pheidole. We suggest ant spines are novel structures among Hymenoptera. We ask how many times spinescence evolved in Pheidole, the extent to which correlations between spinescence and other morphological traits can inform our understanding of spine function and whether spinescence is associated with evolution into high-elevation habitats. We address these questions by mapping spinescence onto a 145-species phylogeny. We determined that spinescence evolved independently at least seven times in Pheidole and that all six extant spinescent lineages are restricted to the Asia-Pacific region. Our results support hypotheses proposing that elongated dorsal spines serve as defence against vertebrate predation and invertebrate attack and that task division is especially pronounced within the worker caste of spinescent species. [ABSTRACT FROM AUTHOR]

Deep-sea sediments constitute a unique archive of ocean change, fueled by a permanent rain of mineral and organic remains from the surface ocean. Until now, paleo-ecological analyses of this archive have been mostly based on information from taxa leaving fossils. In theory, environmental DNA (eDNA) in the sediment has the potential to provide information on non-fossilized taxa, allowing more comprehensive interpretations of the fossil record. Yet, the process controlling the transport and deposition of eDNA onto the sediment and the extent to which it preserves the features of past oceanic biota remains unknown. Planktonic foraminifera are the ideal taxa to allow an assessment of the eDNA signal modification during deposition because their fossils are well preserved in the sediment and their morphological taxonomy is documented by DNA barcodes. Specifically, we re-analyze foraminiferal-specific metabarcodes from 31 deep-sea sediment samples, which were shown to contain a small fraction of sequences from planktonic foraminifera. We confirm that the largest portion of the metabarcode originates from benthic bottom-dwelling foraminifera, representing the in-situ community, but a small portion (<10 %) of the metabarcode can be unambiguously assigned to planktonic taxa. These organisms live exclusively in the surface ocean and the recovered barcodes thus represent an allochthonous "foreign" component deposited with the rain of organic remains from the surface ocean. We take advantage of the planktonic foraminifera portion of the metabarcode to establish to what extent the structure of the surface ocean biota is preserved in sedimentary eDNA. We show that the planktonic DNA is preserved in a range of marine sediment types, the composition of the recovered eDNA metabarcode is replicable and that both the similarity structure and the diversity pattern of the pelagic environment are preserved. These observations pave the way for surveys of seafloor sedimentary eDNA covering the entire spectrum of pelagic biodiversity and its interaction with the climatic history of the oceans. [ABSTRACT FROM AUTHOR]