Abstract. We have collected evidence that the nominal species, Polydora cornuta Bosc 1802, contains at least three separate species in North America. Specimens of P. cornuta were collected in California, Florida, and Maine, raised in the laboratory, and assessed for reproductive compatibility, genetic similarity, gamete characteristics, and developmental rates. Reproductive crosses between each combination of sex and population revealed variable levels of hybridization at the level of fertilization. Percent fertilization was very low for all combinations (0–7%) except for California females crossed with Florida males (42%). In all interpopulation crosses, fertilized eggs arrested in cleavage and no viable larvae were produced. All pairwise comparisons of the studied populations showed significant differences in multiple reproductive traits. Mitochondrial cytochrome oxidase subunit I DNA sequences revealed large differences between Florida and California worms with a maximum likelihood genetic distance of d=0.860, while Florida and Maine worms were d=0.806, and California and Maine d=0.156. California and New Zealand worms were very similar genetically (d=0.010). These data strongly suggest that populations of P. cornuta in North America comprise a cryptic species complex composed of at least three distinct lineages.

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Abstract:We studied lianas in a subtropical wet forest in Puerto Rico to understand how hurricane impacts and past human land-uses interact to affect liana dynamics over a 14-year period. We compared a high-intensity land-use area, where the forest that had been cleared, and used for subsistence agriculture before being abandoned in 1934 then regrew to a low-intensity land-use area, in which there had been only some selective experimental logging by the USDA Forest Service in the 1940s. Prior to our study, both areas were strongly affected by Hurricane Hugo in 1989, and again damaged to a lesser degree by Hurricane Georges in 1998, increasing canopy openness and subsequently increasing tree stem densities. Between 2001 and 2015, changes in the light environment and the recovery of forest structure resulted in roughly a 50% reduction in tree stem densities in the high-intensity land-use area, as recruited saplings naturally thinned. In this area, liana abundance increased by 103%, liana biomass tripled, and occupancy of trees by lianas grew by nearly 50%. In the low-intensity land-use area, juvenile stem densities were stable, and resultantly liana abundance only increased by 33%, liana biomass rose 39%, and the occupancy of trees was constant. Liana flower and fruit production increased over the 14-year interval, and these increases were much greater in the high-intensity land-use quadrats. Results of this study do show how rapid forest tree successional dynamics coincide with liana increases, but the confounding of hurricane effects of disturbance at our site, prevent us from asserting that the increases in liana density and biomass can be attributed to the same causes as those in forests elsewhere in the Neotropics.

Sulfur is an essential nutrient that contributes to cellular redox homeostasis, transcriptional regulation, and translation initiation when incorporated into different biomolecules. Transport and reduction of extracellular sulfate followed by cysteine biosynthesis is a major pathway of bacterial sulfur assimilation. For the opportunistic pathogen Serratia marcescens, function of the cysteine biosynthesis pathway is required for extracellular phospholipase activity and flagellum-mediated surface motility, but little else is known about the influence of sulfur assimilation on the physiology of this organism. In this work, it was determined that an S. marcescens cysteine auxotroph fails to differentiate into hyperflagellated and elongated swarmer cells and that cysteine, but not other organic sulfur molecules, restores swarming motility to these bacteria. The S. marcescens cysteine auxotroph further exhibits reduced transcription of phospholipase, hemolysin, and flagellin genes, each of which is subject to transcriptional control by the flagellar regulatory system. Based on these data and the central role of cysteine in sulfur assimilation, it was reasoned that environmental sulfur availability may contribute to the regulation of these functions in S. marcescens. Indeed, bacteria that are starved for sulfate exhibit substantially reduced transcription of the genes for hemolysin, phospholipase, and the FlhD flagellar master regulator. A global transcriptomic analysis further defined a large set of S. marcescens genes that are responsive to extracellular sulfate availability, including genes that encode membrane transport, nutrient utilization, and metabolism functions. Finally, sulfate availability was demonstrated to alter S. marcescens cytolytic activity, suggesting that sulfate assimilation may impact the virulence of this organism. IMPORTANCE Serratia marcescens is a versatile bacterial species that inhabits diverse environmental niches and is capable of pathogenic interactions with host organisms ranging from insects to humans. This report demonstrates for the first time the extensive impacts that environmental sulfate availability and cysteine biosynthesis have on the transcriptome of S. marcescens. The finding that greater than 1,000 S. marcescens genes are differentially expressed depending on sulfate availability suggests that sulfur abundance is a crucial factor that controls the physiology of this organism. Furthermore, the high relative expression levels for the putative virulence factors flagella, phospholipase, and hemolysin in the presence of sulfate suggests that a sulfur-rich host environment could contribute to the transcription of these genes during infection.

Reproductive crosses between geographically separated populations of the nominal species, Polydora cornuta, support the hypothesis that the Florida/ Gulf of Mexico populations represent a single, potentially interbreeding lineage that is reproductively isolated from West Coast (California) and East Coast (Carolinas to Maine) populations. Previous research has indicated that California populations are reproductively compatible with worms from North Carolina but reproductively isolated from Maine populations. In spite of these species-level differences, all populations of this nominal species deposit egg capsules inside the female’s tube that usually develop into three-chaetiger planktonic larvae measuring about 200 µm in length. Although adelphophagy (feeding upon unfertilized eggs within an egg capsule) has been reported in some populations of P. cornuta and in numerous other spionid polychaetes, the relationship between stored sperm in the female parent and the size of larvae within capsules has not been explored. We raised isolated female P. cornuta from three genetically and reproductively distinct populations (Florida, California and Maine) over a period of about 16 weeks and determined percent fertilization and larval size in successive spawnings over time until the females ran out of stored sperm. As each female used up stored sperm during successive spawnings, the percent of fertilized eggs per capsule declined and larval size at release increased. In some cases, the largest larvae produced by an isolated female were 114% larger than the smallest larvae produced by the same female. Larvae inside capsules containing unfertilized eggs fed upon these eggs and grew larger than larvae that did not have unfertilized eggs to feed upon. The effects of producing larger larvae following stored sperm depletion were completely reversed by transfer of fresh spermatophores to the isolated females. Variable larval size produced by a single female worm (poecilogony) may therefore be a result of stored sperm limitations rather than a genetically determined reproductive strategy in this species complex.