Scaling of Olfactory Antennae of the Terrestrial Hermit Crabs \u3cem\u3eCoenobita rugosus\u3c/em\u3e and \u3cem\u3eCoenobita perlatus\u3c/em\u3e During Ontogeny

Although many lineages of terrestrial crustaceans have poor olfactory capabilities, crabs in the family Coenobitidae, including the terrestrial hermit crabs in the genus Coenobita, are able to locate food and water using olfactory antennae (antennules) to capture odors from the surrounding air. Terrestrial hermit crabs begin their lives as small marine larvae and must find a suitable place to undergo metamorphosis into a juvenile form, which initiates their transition to land. Juveniles increase in size by more than an order of magnitude to reach adult size. Since odor capture is a process heavily dependent on the size and speed of the antennules and physical properties of the fluid, both the transition from water to air and the large increase in size during ontogeny could impact odor capture. In this study, we examine two species of terrestrial hermit crabs, Coenobita perlatus H. Milne-Edwards and Coenobita rugosus H. Milne-Edwards, to determine how the antennule morphometrics and kinematics of flicking change in comparison to body size during ontogeny, and how this scaling relationship could impact odor capture by using a simple model of mass transport in flow. Many features of the antennules, including the chemosensory sensilla, scaled allometrically with carapace width and increased slower than expected by isometry, resulting in relatively larger antennules on juvenile animals. Flicking speed scaled as expected with isometry. Our mass-transport model showed that allometric scaling of antennule morphometrics and kinematics leads to thinner boundary layers of attached fluid around the antennule during flicking and higher odorant capture rates as compared to antennules which scaled isometrically. There were no significant differences in morphometric or kinematic measurements between the two species

Metapopulation dominance and genomic-island acquisition of Bradyrhizobium with superior catabolic capabilities

Root nodule-forming rhizobia exhibit a bipartite lifestyle, replicating in soil and also within plant cells where they fix nitrogen for legume hosts. Host control models posit that legume hosts act as a predominant selective force on rhizobia, but few studies have examined rhizobial fitness in natural populations. Here, we genotyped and phenotyped Bradyrhizobium isolates across more than 800 km of the native Acmispon strigosus host range. We sequenced chromosomal genes expressed under free-living conditions and accessory symbiosis loci expressed in planta and encoded on an integrated ‘symbiosis island’ (SI). We uncovered a massive clonal expansion restricted to the Bradyrhizobium chromosome, with a single chromosomal haplotype dominating populations, ranging more than 700 km, and acquiring 42 divergent SI haplotypes, none of which were spatially widespread. For focal genotypes, we quantified utilization of 190 sole-carbon sources relevant to soil fitness. Chromosomal haplotypes that were both widespread and dominant exhibited superior growth on diverse carbon sources, whereas these patterns were not mirrored among SI haplotypes. Abundance, spatial range and catabolic superiority of chromosomal, but not symbiosis genotypes suggests that fitness in the soil environment, rather than symbiosis with hosts, might be the key driver of Bradyrhizobium dominance

Metapopulation dominance and genomic-island acquisition of Bradyrhizobium with superior catabolic capabilities

Root nodule-forming rhizobia exhibit a bipartite lifestyle, replicating in soil and also within plant cells where they fix nitrogen for legume hosts. Host control models posit that legume hosts act as a predominant selective force on rhizobia, but few studies have examined rhizobial fitness in natural populations. Here, we genotyped and phenotyped Bradyrhizobium isolates across more than 800 km of the native Acmispon strigosus host range. We sequenced chromosomal genes expressed under free-living conditions and accessory symbiosis loci expressed in planta and encoded on an integrated ‘symbiosis island’ (SI). We uncovered a massive clonal expansion restricted to the Bradyrhizobium chromosome, with a single chromosomal haplotype dominating populations, ranging more than 700 km, and acquiring 42 divergent SI haplotypes, none of which were spatially widespread. For focal genotypes, we quantified utilization of 190 sole-carbon sources relevant to soil fitness. Chromosomal haplotypes that were both widespread and dominant exhibited superior growth on diverse carbon sources, whereas these patterns were not mirrored among SI haplotypes. Abundance, spatial range and catabolic superiority of chromosomal, but not symbiosis genotypes suggests that fitness in the soil environment, rather than symbiosis with hosts, might be the key driver of Bradyrhizobium dominance

Morphometric and Kinematics data accompanying "Scaling of olfactory antennae of the terrestrial hermit crabs Coenobita rugosus and Coenobita perlatus during ontogeny"

<p>These data accompany the manuscript "Scaling of olfactory antennae of the terrestrial hermit crabs <em>Coenobita rugosus</em> and <em>Coenobita perlatus</em> during ontogeny" submitted for publication. </p> <p><strong>morphdataforR.csv</strong> contains the raw morphometric data measured from scanning electron micrographs, including ID number, species name, carapace width, antennule metrics (width, length and thickness), aesthetasc metrics (width, length, thickness, insertion angle), and number of aesthetascs.</p> <p><strong>hermit_veldata2-1.csv</strong> contains the raw kinematic data measured from videos of hermit crab flicking their antennules, including ID number, species name, number of flicks, downstroke speed and duration, and return stroke speed and duration. </p

Fungal Diversity Associated with Hawaiian Drosophila Host Plants

Hawaiian Drosophila depend primarily, sometimes exclusively, on specific host plants for oviposition and larval development, and most specialize further on a particular decomposing part of that plant. Differences in fungal community between host plants and substrate types may establish the basis for host specificity in Hawaiian Drosophila. Fungi mediate decomposition, releasing plant micronutrients and volatiles that can indicate high quality substrates and serve as cues to stimulate oviposition. This study addresses major gaps in our knowledge by providing the first culture-free, DNA-based survey of fungal diversity associated with four ecologically important tree genera in the Hawaiian Islands. Three genera, Cheirodendron, Clermontia, and Pisonia, are important host plants for Drosophila. The fourth, Acacia, is not an important drosophilid host but is a dominant forest tree. We sampled fresh and rotting leaves from all four taxa, plus rotting stems from Clermontia and Pisonia. Based on sequences from the D1/D2 domain of the 26S rDNA gene, we identified by BLAST search representatives from 113 genera in 13 fungal classes. A total of 160 operational taxonomic units, defined on the basis of ≥97% genetic similarity, were identified in these samples, but sampling curves show this is an underestimate of the total fungal diversity present on these substrates. Shannon diversity indices ranged from 2.0 to 3.5 among the Hawaiian samples, a slight reduction compared to continental surveys. We detected very little sharing of fungal taxa among the substrates, and tests of community composition confirmed that the structure of the fungal community differed significantly among the substrates and host plants. Based on these results, we hypothesize that fungal community structure plays a central role in the establishment of host preference in the Hawaiian Drosophila radiation

Fungal Diversity Associated with Hawaiian Drosophila Host Plants

Hawaiian Drosophila depend primarily, sometimes exclusively, on specific host plants for oviposition and larval development, and most specialize further on a particular decomposing part of that plant. Differences in fungal community between host plants and substrate types may establish the basis for host specificity in Hawaiian Drosophila. Fungi mediate decomposition, releasing plant micronutrients and volatiles that can indicate high quality substrates and serve as cues to stimulate oviposition. This study addresses major gaps in our knowledge by providing the first culture-free, DNA-based survey of fungal diversity associated with four ecologically important tree genera in the Hawaiian Islands. Three genera, Cheirodendron, Clermontia, and Pisonia, are important host plants for Drosophila. The fourth, Acacia, is not an important drosophilid host but is a dominant forest tree. We sampled fresh and rotting leaves from all four taxa, plus rotting stems from Clermontia and Pisonia. Based on sequences from the D1/D2 domain of the 26S rDNA gene, we identified by BLAST search representatives from 113 genera in 13 fungal classes. A total of 160 operational taxonomic units, defined on the basis of ≥97% genetic similarity, were identified in these samples, but sampling curves show this is an underestimate of the total fungal diversity present on these substrates. Shannon diversity indices ranged from 2.0 to 3.5 among the Hawaiian samples, a slight reduction compared to continental surveys. We detected very little sharing of fungal taxa among the substrates, and tests of community composition confirmed that the structure of the fungal community differed significantly among the substrates and host plants. Based on these results, we hypothesize that fungal community structure plays a central role in the establishment of host preference in the Hawaiian Drosophila radiation

Neighbor joining phylogenetic tree.

<p>The tree is composed of fungal sequences generated in this study and their respective closest BLAST hits. Branches with bootstrap support ≥70 shown in bold. The two colored rings surrounding the tree indicate the plant genus (innermost ring) and the type of substrate (second ring) from which the fungal sequences in this study were obtained. Fungal genera are indicated outside the substrate ring. Fungal classes are indicated by the grey outermost ring. Classes are abbreviated as follows: Aga, Agaricomycetes; Ags, Agaricostilbomycetes; Art, Arthoniomycetes; Atc, Atractiellomycetes; Dot, Dothideomycetes; Eur, Eurotiomycetes; Exo, Exobasidiomycetes; Leo, Leotiomycetes; Mic, Microbotryomycetes; Sac, Saccharomycetes; Sor, Sordariomyctetes; Tap, Taphrinomycetes; Tre, Tremellomycetes. Classes that came out paraphyletic on the tree (Dot and Art; Tre and Aga) are indicated with a black border around the grey bar.</p

Summary of substrate and host plant use in Hawaiian <i>Drosophila</i>.

<p>Phylogenetic relationships of major lineages in Hawaiian <i>Drosophila</i> are shown with substrate type mapped onto the tree (after <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0040550#pone.0040550-OGrady4" target="_blank">[28]</a>). Rearing record data (after <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0040550#pone.0040550-Magnacca1" target="_blank">[32]</a>, updated with <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0040550#pone.0040550-Magnacca2" target="_blank">[77]</a>) are shown in the pie charts. The first column depicts substrate types for each of the main clades (AMC, PNA and modified mouthpart), the second column shows host plant family. While these analyses are not entirely comparable because not all taxa in the phylogeny have rearing data and not all reared species were sampled for the phylogeny, they do show the same trends. First, there is a major shift from bark and stems (black) in the basal lineages to leaves (green) in the AMC and part of the modified mouthparts clades. Taxa using multiple substrate types (e.g., stems and leaves) are shown in red. Second, there is much greater diversity in host plant family usage in the picture wing and modified mouthparts clades owing to the radiation on Araliaceae within the AMC clade. The three host plant families examined in this study are color-coded on the pie charts are follows: Araliaceae (<i>Cheirodendron</i>, green), Campanulaceae (<i>Clermontia</i>, blue), and Nyctagenaceae (<i>Pisonia</i>, orange). Taxa using multiple host plant families are shown in red.</p

Diversity summary statistics for fungal communities.

<p>Diversity is described for ten plant/substrate types, based on an OTU definition of 97% genetic similarity. (a) The number of OTUs identified in the sample. (b) The non-parametric Shannon diversity index, <i>H</i>_NP. (c) Chao1 diversity.</p

Rarefaction analyses of observed fungal OTU richness within ten plant/substrate sample types.

<p>OTUs were defined at the 97% genetic similarity cut-off using the furthest-neighbor clustering method in <i>mothur</i>.</p