Patterns and drivers of aquatic invertebrate diversity across an arid biome

Managing and restoring faunal diversity across large areas requires an understanding of the roles of connectivity and dispersal in driving community patterns. We sought to determine the influence of connectivity, water regime, water source, geographical location, and dispersal traits on patterns of aquatic invertebrate diversity across a continent‐wide arid biome. We compiled data on freshwater invertebrate assemblages from sites spanning the breadth of arid Australia. Univariate analyses (analysis of variance and rarefaction) revealed that alpha and gamma diversity across sites decreased as latitude increased. Multivariate analyses (ordination and analysis of similarity) revealed that community composition had considerable fidelity to geographic regions. Hydrological connectivity was strongly associated with riverine community composition although water rarely flowed (often less than annually). Hydrologically isolated sites (springs and rockholes) supported communities that were markedly dissimilar to hydrologically connected sites, and to each other. We investigated the influence of dispersal on diversity patterns by examining distance decay relationships for each of four dispersal trait groups (obligate aquatic and passive, weak, and strong aerial dispersers) on the basis of geodesic (shortest path) distances between pairs of sites and Mantel tests. We did not detect clear differences between dispersal traits and distance decay relationships at the continental scale, even for the two groups with the lowest dispersal ability (obligate aquatics and passive dispersers). Our results suggest that the loss of hydrological connectivity from water developments in arid lands (for example, the impoundment of intermittent rivers) is likely to affect macroinvertebrates. However, the exact flow mechanisms underlying such changes remain to be determined.     

Review of five species of cyclocoelids (Digenea: Cyclocoelidae) from aquatic birds in Mexico with notes on their interspecific variation

Based on a morphological approach, five species of cyclocoelids (Digenea: Cyclocoelidae) are revised based on material from birds in Mexico. The species studied are: Cyclocoelum cf. leidyi Harrah, 1922 from the black-necked stilt Himantopus mexicanus Müller (Recurvirostridae); Cyclocoelum mutabile (Zeder, 1800) from the northern jacana Jacana spinosa L. (Jacanidae) and the willet Tringa semipalmata Gmelin (Scolopacidae); Cyclocoelum pseudomicrostomum Harrah, 1922 from the American coot Fulica americana Gmelin (Rallidae); Selfcoelum lamothei Blend & Dronen, 2008, from the long-billed curlew Numenius americanus Bechstein (Scolopacidae); and Neohaematotrephus arayae Zamparo, Brooks, Causey & Rodriguez, 2003 from J. spinosa. New morphological data, illustrations and measurements are presented for these trematodes. Three species, insufficiently described, i.e. C. cf. leidyi, C. mutabile and C. pseudomicrostomum, are redescribed in detail. Our results indicate morphological variation in some important features used in the diagnosis of Cyclocoelum Brandes, 1892 (i.e. the presence or absence of oral sucker, the position of the genital pore relative to the pharynx, and the posterior extension of the uterus) and Selfcoelum Dronen, Gardner & Jiménez, 2006 (i.e. anterior extension of vitelline follicles). Finally, this study provides the first molecular data for the large subunit of the ribosomal RNA (28S rRNA) gene for N. arayae.     

The plant hormone salicylic acid interacts with the mechanism of anti‐herbivory conferred by fungal endophytes in grasses

The plant hormone salicylic acid (SA) is recognized as an effective defence against biotrophic pathogens, but its role as regulator of beneficial plant symbionts has received little attention. We studied the relationship between the SA hormone and leaf fungal endophytes on herbivore defences in symbiotic grasses. We hypothesize that the SA exposure suppresses the endophyte reducing the fungal‐produced alkaloids. Because of the role that alkaloids play in anti‐herbivore defences, any reduction in their production should make host plants more susceptible to herbivores. Lolium multiflorum plants symbiotic and nonsymbiotic with the endophyte Epichloë occultans were exposed to SA followed by a challenge with the aphid Rhopalosiphum padi. We measured the level of plant resistance to aphids, and the defences conferred by endophytes and host plants. Symbiotic plants had lower concentrations of SA than did the nonsymbiotic counterparts. Consistent with our prediction, the hormonal treatment reduced the concentration of loline alkaloids (i.e., N‐formyllolines and N‐acetylnorlolines) and consequently decreased the endophyte‐conferred resistance against aphids. Our study highlights the importance of the interaction between the plant immune system and endophytes for the stability of the defensive mutualism. Our results indicate that the SA plays a critical role in regulating the endophyte‐conferred resistance against herbivores.     

The Xerobranching Response Represses Lateral Root Formation When Roots Are Not in Contact with Water

1. Download high-res image (212KB)
2. Download full-size image

     

Large Plankton Enhance Heterotrophy Under Experimental Warming in a Temperate Coastal Ecosystem

Microbes are key players in oceanic carbon fluxes. Temperate ecosystems are seasonally variable and thus suitable for testing the effect of warming on microbial carbon fluxes at contrasting oceanographic conditions. In four experiments conducted in February, April, August and October 2013 in coastal NE Atlantic waters, we monitored microbial plankton stocks and daily rates of primary production, bacterial heterotrophic production and respiration at in situ temperature and at 2 and 4°C over ambient values during 4-day incubations. Ambient total primary production (TPP) exceeded total community respiration (< 200 µm, TR) in winter and fall but not in spring and summer. The bacterial contribution to ecosystem carbon fluxes was low, with bacterial production representing on average 6.9 ± 3.2% of TPP and bacterial respiration (between 0.8 and 0.2 µm) contributing on average 35 ± 7% to TR. Warming did not result in a uniform increase in the variables considered, and most significant effects were found only for the 4°C increase. In the summer and fall experiments, under warm and nutrient-deficient conditions, the net TPP/TR ratio decreased by 39 and 34% in the 4°C treatment, mainly due to the increase in respiration of large organisms rather than bacteria. Our results indicate that the interaction of temperature and substrate availability in determining microbial carbon fluxes has a strong seasonal component in temperate planktonic ecosystems, with temperature having a more pronounced effect and generating a shift toward net heterotrophy under more oligotrophic conditions as found in summer and early fall.