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1. Effects of predation pressure and prey density on short‐term indirect interactions between two prey species that share a common predator

   https://doi.org/10.1111/een.12855  

   Emery, Sara E. ; Mills, Nicholas J. ( March 2020 , Ecological Entomology)

   1. Generalist predators are important contributors to reliable conservation biological control. Indirect interactions between prey species that share a common generalist predator can influence both community dynamics and the efficacy of biological control.

   2. Laboratory cage experiments investigated the impact of the combined consumptive and non‐consumptive effects of predation by adultHippodamia convergensas a shared predator on the population growth and relative abundance ofAcyrthosiphon pisumandAphis gossypiias prey species. Predation pressure and prey density were varied.

   3. At low predation pressure the indirect interaction between aphid species was asymmetrical with a proportionally greater negative impact of predation onA. gossypiithan onA. pisum. At intermediate predation pressure, the indirect interaction became symmetrical. At high predation pressure and higher levels of prey density, it was asymmetrical with greater negative impact onA. pisum, often driven to local extinction whileA. gossypiipopulations persisted.

   4. A linear mixed‐effects model including early population growth of both aphid species and predation pressure explained 96% and 92% of the variation in the population growth ofA. pisumandA. gossypii, respectively, over an 8‐day period. The overall effect of shared predation on the indirect interaction between the two aphid species is best described as apparent commensalism, whereA. pisumbenefited from early population growth ofA. gossypii, whileA. gossypiiwas unaffected by early population growth ofA. pisum. Considering these indirect interactions is important for conservation biological control efforts to be successful.

    

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2. HT proteins contribute to S‐ RN ase‐independent pollen rejection in Solanum

   https://doi.org/10.1111/tpj.13416  

   Tovar‐Méndez, Alejandro ; Lu, Lu ; McClure, Bruce ( February 2017 , The Plant Journal)

   Plants have mechanisms to recognize and reject pollen from other species. Although widespread, these mechanisms are less well understood than the self‐incompatibility (SI) mechanisms plants use to reject pollen from close relatives. Previous studies have shown that some interspecific reproductive barriers (IRBs) are related toSIin the Solanaceae. For example, the pistilSIproteins S‐RNase andHTprotein function in a pistil‐sideIRBthat causes rejection of pollen from self‐compatible (SC) red/orange‐fruited species in the tomato clade. However, S‐RNase‐independentIRBs also clearly contribute to rejecting pollen from these species. We investigated S‐RNase‐independent rejection ofSolanum lycopersicumpollen bySCSolanum pennelliiLA0716,SC.Solanum habrochaitesLA0407, andSCSolanum arcanumLA2157, which lack functional S‐RNase expression. We found that all three accessions expressHTproteins, which previously had been known to function only in conjunction with S‐RNase, and then usedRNAi to test whether they also function in S‐RNase‐independent pollen rejection. SuppressingHTexpression inSCS. pennelliiLA0716 allowsS. lycopersicumpollen tubes to penetrate farther into the pistil inHTsuppressed plants, but not to reach the ovary. In contrast, suppressingHTexpression inSC.Solanum habrochaitesLA0407 and inSCS. arcanumLA2157 allowsS. lycopersicumpollen tubes to penetrate to the ovary and produce hybrids that, otherwise, would be difficult to obtain. Thus,HTproteins are implicated in both S‐RNase‐dependent and S‐RNase‐independent pollen rejection. The results support the view that overall compatibility results from multiple pollen–pistil interactions with additive effects.

    

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3. Hydrodynamic role of substrate attachment in shaping the suspension‐feeding current created by the marine gastropod Crepidula fornicata

   https://doi.org/10.1111/ivb.12383  

   Jiang, Houshuo ; Pechenik, Jan A. ( November 2022 , Invertebrate Biology)

   As in lamellibranch bivalves, individuals of the common Atlantic slippersnailCrepidula fornicatabeat cilia on their gill filaments to produce a suspension‐feeding current. Having only one shell and no siphons with which to direct water flow, however, individuals ofC. fornicatamust adhere to a solid substrate to facilitate normal feeding. Thus, what hydrodynamic role does substrate attachment play in producing, regulating, and directing the suspension‐feeding current for this species? Here, a combined particle image velocimetry and computational fluid dynamics study was conducted to address this question. Three findings were obtained: (1) Juveniles ofC. fornicata(shell length 6.0–10.6 mm) whose foot was attached to a solid surface generated a strong, fan‐like exhalant current and an almost equally strong, convergent inhalant current, both being spatially well extended; (2) juveniles ofC. fornicatathat were prevented from adhering to any surface also generated a strong, fan‐like exhalant current but a much weaker and spatially limited inhalant current; and (3) whether or not they were attached to a solid surface, juveniles ofC. fornicatahad almost the same performance or system characteristics of the ciliary water pump, including the relationship between flow pressure rise Δpacross the ciliary zone and volume flow rateQ, pump resistance Δp/Q, and pressure coefficient for laminar flowC_p,l. These results indicate that the primary hydrodynamic effect of substrate attachment inC. fornicatais to form a complete inhalant chamber with a narrowed opening, such that negative flow pressure develops in the inhalant chamber, and a strong, convergent, spatially well‐extended inhalant current is generated to effectively bring in food particles from farther distances and to reduce refiltration of the outflowing water. Finally, ecological trade‐offs are discussed regarding the two distinct shell configuration strategies: (1) that of the single‐shelledC. fornicata, with only a naturally formed exhalant chamber and opening but not a morphologically defined inhalant chamber and opening, and (2) that of two‐shelled bivalves, with naturally formed exhalant and inhalant chambers.

    

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4. Community theory: Testing environmental stress models

   https://doi.org/10.1111/ele.14240  

   Menge, Bruce A. ( August 2023 , Ecology Letters)

   Intensifying climate change and an increasing need for understanding its impacts on ecological communities places new emphasis on testing environmental stress models (ESMs). Using a prior literature search plus references from a more recent search, I evaluated empirical support forESMs, focusing on whether consumer pressure on prey decreased (consumer stress model;CSM) or increased (prey stress model;PSM) with increasing environmental stress. Applying the criterion that testingESMsrequires conducting research at multiple sites along environmental stress gradients, the analysis found thatCSMswere most frequent, with ‘No Effect’ andPSMsoccurring at low but similar frequencies. This result contrasts to a prior survey in which ‘No Effect’ studies were most frequent, thus suggesting that consumers are generally more suppressed by stress than prey. Thus, increased climate change‐induced environmental stress seems likely to reduce, not increase impacts of consumers on prey more often than the reverse

    

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5. Tooth development and replacement in the Atlantic Cutlassfish, Trichiurus lepturus , with comparisons to other Scombroidei

   https://doi.org/10.1002/jmor.20919  

   Bemis, Katherine E. ; Burke, Samantha M. ; St. John, Carl A. ; Hilton, Eric J. ; Bemis, William E. ( December 2018 , Journal of Morphology)

   Atlantic Cutlassfish,Trichiurus lepturus, have large, barbed, premaxillary and dentary fangs, and sharp dagger‐shaped teeth in their oral jaws. Functional teeth firmly ankylose to the dentigerous bones. We used dry skeletons, histology, SEM, and micro‐CT scanning to study 92 specimens ofT. lepturusfrom the western North Atlantic to describe its dentition and tooth replacement. We identified three modes of intraosseous tooth replacement inT. lepturusdepending on the location of the tooth in the jaw. Mode 1 relates to replacement of premaxillary fangs, in which new tooth germs enter the lingual surface of the premaxilla, develop horizontally, and rotate into position. We suggest that growth of large fangs in the premaxilla is accommodated by this horizontal development. Mode 2 occurs for dentary fangs: new tooth germs enter the labial surface of the dentary, develop vertically, and erupt into position. Mode 3 describes replacement of lateral teeth, in which new tooth germs enter a trench along the crest of the dentigerous bone, develop vertically, and erupt into position. Such distinct modes of tooth replacement in a teleostean species are unknown. We compared modes of replacement inT. lepturusto 20 species of scombroids to explore the phylogenetic distribution of these three replacement modes. Alternate tooth replacement (in which new teeth erupt between two functional teeth), ankylosis, and intraosseous tooth development are plesiomorphic to Bluefish + other Scombroidei. Our study highlights the complexity and variability of intraosseous tooth replacement. Within tooth replacement systems, key variables include sites of formation of tooth germs, points of entry of tooth germs into dentigerous bones, coupling of tooth germ migration and bone erosion, whether teeth develop horizontally or immediately beneath the tooth to be replaced, and how tooth eruption and ankylosis occur. Developmentally different tooth replacement processes can yield remarkably similar dentitions.

    

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