Soil functional resistance and stability are linked to different ecosystem properties

The functional resistance and resilience of soils from across the South Island of New Zealand were assessed. Soils were collected from under varying land‐uses (pasture, pine forest, native forest) at each of four different locations (Hokitika, Craigieburn, Eyrewell, Orton Bradley Park). Soil function was measured using carbon utilization profiles (MicroResp technique), and responses to freeze‐thaw disturbance assessed in a multivariate approach. Resistance was defined as the amount of change in functional profiles (multivariate distance) before, and then 10 h after, disturbance. Resilience was defined as the stability in ecosystem function over time (6 sample points spanning 17 days after initial freeze‐thaw disturbance). The functional resistance of soils was not linked to land‐use nor sampling location (permanova P > 0.05) but was negatively correlated with soil Olsen‐P levels (biological‐environmental matching (BIO‐ENV test); ρ = 0.604, P = 0.04). Secondary factors associated with soil organic matter status were associated with functional resistance in soil of low Olsen‐P. This was explicitly tested by repeating the experiment in soils collected from a long‐term P fertilizer management trial; functional resistance remained linked to the underlying P status of the soils (P = 0.002). The functional stability of soil (post‐disturbance) was associated with long‐term rainfall (canonical analysis on principal coordinates – CAP analysis; P = 0.039); soils from high rainfall sites were more stable after disturbance. The results show that variables linked to functional resistance and resilience in soils are different. Furthermore, resilience was not correlated with resistance, or with measures of functional diversity (e.g. evenness of substrate mineralization). Alteration of the P status of soils is likely to impact on the capacity of soils to rapidly respond to disturbance, whereas drivers of climate, such as global warming, may impact soil functional resilience.     

The role of Rdl in resistance to phenylpyrazoles in Drosophila melanogaster

Extensive use of older generation insecticides may result in pre-existing cross-resistance to new chemical classes acting at the same target site. Phenylpyrazole insecticides block inhibitory neurotransmission in insects via their action on ligand-gated chloride channels (LGCCs). Phenylpyrazoles are broad-spectrum insecticides widely used in agriculture and domestic pest control. So far, all identified cases of target site resistance to phenylpyrazoles are based on mutations in the Rdl (Resistance to dieldrin) LGCC subunit, the major target site for cyclodiene insecticides. We examined the role that mutations in Rdl have on phenylpyrazole resistance in Drosophila melanogaster, exploring naturally occurring variation, and generating predicted resistance mutations by mutagenesis. Natural variation at the Rdl locus in inbred strains of D. melanogaster included gene duplication, and a line containing two Rdl mutations found in a highly resistant line of Drosophila simulans. These mutations had a moderate impact on survival following exposure to two phenylpyrazoles, fipronil and pyriprole. Homology modelling suggested that the Rdl chloride channel pore contains key residues for binding fipronil and pyriprole. Mutagenesis of these sites and assessment of resistance in vivo in transgenic lines showed that amino acid identity at the Ala³⁰¹ site influenced resistance levels, with glycine showing greater survival than serine replacement. We confirm that point mutations at the Rdl 301 site provide moderate resistance to phenylpyrazoles in D. melanogaster. We also emphasize the beneficial aspects of testing predicted mutations in a whole organism to validate a candidate gene approach.     

Genetically engineered resistance to organophosphate herbicides provides a new scoreable and selectable marker system for transgenic plants

Organophosphate hydrolase (OPH, E.C. 3.1.8.1; encoded by the bacterial opd gene) provides a new scoreable and selectable genetic marker system for use in plant cell culture and regenerated plant tissue. OPH hydrolyzes a wide range of substrates that produce visually detectable products, which can be readily quantified in biological tissues. A variety of different OP compounds, both herbicides and pesticides, have been identified as acceptable enzymatic substrates, which can be used to generate transgenic markers for various types of plant tissues. For example, transgenic leaf tissue was easily differentiated from non-transgenic tissue by a simple fluorescent assay utilizing the OP insecticide coroxon. Transformed callus and intact whole seed could be easily distinguished from non-transformed tissue using novel non-destructive methods which allowed callus or seeds to grow and/or to germinate after phenotypic scoring with non-herbicidal OP insecticides such as paraoxon. In addition to being used as a scoreable phenotypic markers with various OP pesticides, the OP compounds Haloxon and Bensulide (Bensumec-4LF) were effective as positive selection agents for callus and germinating seeds.     

Phenotypic and genetic patterns of resistance to the pathogen Phakopsora pachyrhizi in populations of Glycine canescens

Summary Phenotypic patterns of resistance to nine races of the pathogen Phakopsora pachyrhizi (soybean rust) in two natural populations of Glycine canescens were determined. In both populations there was considerable variability both within and between different host lines in their resistance or susceptibility to the nine different pathogen races. The genetic basis of these patterns of resistance was analyzed through an extensive series of crosses. In both host populations resistance was conditioned by single dominant genes with major phenotypic effects. One, two or three such genes were present in each host line. Using the principles of the gene-for-gene hypothesis, knowledge about the number of resistance genes present in each host line and by cross comparison of the phenotypic patterns of disease resistance detected in each line, estimates were made of the number of resistance genes or alleles present in each population of G. canescens. The two populations contained a minimum of 10 and 12 resistance genes. The relevance of these results to agriculture is discussed briefly.     

Morphological,phytochemical and genetic diversity of threatened Polygonatum verticillatum (L.) All. populations of different altitudes and habitat types in Himalayan region

Polygonatum verticillatum (L.) All. is an important medicinal herb that belongs to the family Asparagaceae. The rhizome of the species is used in Chyavanprash preparation and several other ayurvedic formulations. Numerous active constituents like saponins, alkaloids, phytohormones, flavonoids, antioxidants, lysine, serine, aspartic acid, diosgenin, β-sitosterol, etc. have been reported from this species. In this study, morphological, phytochemical, antioxidant and genetic variations of 11 distant populations of P. verticillatum were measured. Considerably (P < 0.05) higher variations were recorded among different populations of P. verticillatum using morphological, phytochemical and genetic diversity parameters. AGFW (above ground fresh weights); flavonols, FRAP (Ferric ion reducing antioxidant power) and NO (Nitric Oxide scavenging activity) were recorded maximum in Kafni population. Similarly, a significantly higher above and below ground dry weight was recorded in Mayawati and Surmoli populations respectively. Maximum phenolic content, tannins, and DPPH (2,2-diphenyl-1-picrylhydrazyl) activity were recorded in Milam population. A total of 165 individuals from 11 populations were assessed for genetic diversity using inter-simple sequence repeats (ISSR) marker. High genetic diversity (He = 0.35) was recorded in Himkhola and Surmoli populations while it was observed minimum (0.28) in the Mayawati population. Altitude showed a significant positive correlation with tannins (r = 0.674; P < 005) and DPPH (r = 0.820; P < 0.01). Phenol content exhibited a considerably positive relationship with He (r = 0.606; P < 0.05) and BGFW (r = 0.620; P < 0.05), flavonol displayed a positive correlation with Pp% (r = 0.606; P < 0.05). The population structure of P. verticillatum, exhibited that the optimal value of the K was 3 for its populations as determined by the ΔK statistic structure. Among populations, the amount of gene flow is higher (Nm = 1.717) among all sites. Hence, it can be concluded that P. verticillatum populations possess considerable variability in the collected populations. Likewise, the populations from Kafni, Satbunga and Himkhola with higher morphological, phytochemicals and genetic variability were prioritized and therefore recommended for cultivation and mass multiplication to meet the industrial demand for target species.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12298-021-01044-9.     

棉铃虫对转Bt基因棉的抗性及其治理策略研究进展棉铃虫对转Bt基因棉的抗性及其治理策略研究进展

简述了苏云金杆菌Bacillus thuringiensis（Bt）毒素的作用方式及杀虫机理,分析了Bt棉种植过程中面临的生态风险。综述了昆虫对Bt毒素的抗性机理、监测方法及治理策略方面的研究进展。棉铃虫对Bt棉的抗性可能主要与中肠上皮细胞膜上的特异性结合受体中结合位点的改变有关。在多种抗性治理策略中,庇护所策略被公认为是目前最有效的并已广泛采用的抗性治理措施。应针对Bt棉在我国的种植情况,在棉铃虫还未在田间表现出抗性以前,制定合理的抗性预防、治理措施。     

Increased pathogen resistance and yield in transgenic plants expressing combinations of the modified antimicrobial peptides based on indolicidin and magainin

Reverse peptide of indolicidin (Rev4), a 13-residue peptide based on the sequence of indolicidin, has been shown to possess both strong antimicrobial and protease inhibitory activities in vitro. To evaluate its efficacy in vivo, we produced and evaluated transgenic tobacco (Nicotiana tabacum L.) and Arabidopsis thaliana [(L.) Heynh.] plants expressing Rev4 with different signal peptide sequences for pathogen resistance. All transgenic plants showed normal growth and development, an indication of no or low cytotoxicity of the peptide. Furthermore, the transgenic plants exhibited elevated resistance to three bacterial and two oomycete pathogens. Interestingly, tobacco plants expressing Rev4 displayed enhanced yield compared to the control as indicated by an increased biomass production by as much as 34% in two field trials. When Rev4 was coexpressed with another antimicrobial peptide, Myp30, the disease resistance levels in the transgenic Arabidopsis were enhanced. These findings suggest the potential of using these peptides to protect plants from microbial pathogens and to enhance yield.     

Host mating system and the spread of a disease-resistant allele in a population

The model presented here modifies a susceptible-infected (SI) host–pathogen model to determine the influence of mating system on the outcome of a host–pathogen interaction. Both deterministic and stochastic (individual-based) versions of the model were used. This model considers the potential consequences of varying mating systems on the rate of spread of both the pathogen and resistance alleles within the population. We assumed that a single allele for disease resistance was sufficient to confer complete resistance in an individual, and that both homozygote and heterozygote resistant individuals had the same mean birth and death rates. When disease invaded a population with only an initial small fraction of resistant genes, inbreeding (selfing) tended to increase the probability that the disease would soon be eliminated from a small population rather than become endemic, while outcrossing greatly increased the probability that the population would become extinct due to the disease.     

应用高剂量/庇护所策略管理Bt作物抗性的三个基本假设：综述与展望

目前, 抗虫转基因作物的抗性管理方法主要是高剂量/庇护所策略。该策略的有效性取决于3个基本的假设条件：（1）抗虫转基因作物（Bt作物）表达出高剂量的杀虫蛋白, 该剂量使得靶标害虫对Bt杀虫蛋白的抗性表现型为功能性完全隐性或近于完全隐性, 进而使得Bt作物可以杀死几乎所有的抗性杂合个体和所有的敏感性个体;（2）靶标害虫种群的Bt抗性基因起始频率处于很低的水平;（3）源自转基因作物田和非转基因作物田(庇护所)的成虫在田间随机混合并交配。这3个假设必须同时满足, 缺一不可。本文就这3个假设的理论基础和经验研究的进展进行了综合论述, 并着重讨论了随机交配假设的最新研究进展以及今后的研究方向和方法。     

Frequency of alleles conferring resistance to Bacillus thuringiensis maize in Louisiana populations of the southwestern corn borer

Transgenic maize [Zea mays L. (Poaceae)] expressing Bacillus thuringiensis proteins (Bt maize) has become the most important tool for managing stalk borers in maize in the USA. The current strategy for delaying the evolution of resistance in target insects for Bt maize is referred to as high dose/refuge strategy. A key requirement of the strategy is that initial resistance allele frequencies in field insect populations are low (e.g., <0.001). More than 200 iso‐line families of the southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae), a major target stalk borer pest of Bt maize, were developed from Louisiana populations and evaluated for Bt resistance using a modified F₂ screening method during 2005. No major resistance alleles were detected in these populations. The results showed that the expected Bt resistance allele frequency in the Louisiana populations was <0.0035 with 95% probability and a detection power of 83.9 ± 0.6%. The F₂ screen indicates that Bt resistance allele frequencies in D. grandiosella are low among the Louisiana populations and should meet the rare resistance allele requirement of the ‘high dose/refuge’ strategy.     

Ecosystem engineering by larvae of net-spinning stream caddisflies creates a habitat on the upper surface of stones for mayfly nymphs with a low resistance to flows

1. Field and laboratory experiments were conducted to examine the effect of larval retreats of the net‐spinning stream caddisfly Hydropsyche orientalis on abundances on flow exposed stone surfaces of nymphs of the mayfly Ephemerella setigera, which prefer slow flow conditions, and to determine whether the construction of retreats ameliorated the habitat and made it more suitable for E. setigera. 2. In a field experiment, artificial substrates with retreats of H. orientalis had higher E. setigera abundances than substrates lacking retreats. In addition, abundances of E. setigera nymphs increased significantly with those of H. orientalis larvae on the upper surface of boulders in streams. 3. The drift loss of E. setigera from plates, with and without retreats, was investigated along a current velocity gradient in a laboratory channel experiment. Nearly all E. setigera nymphs remained on the plates with retreats, even at the highest current velocity. In contrast, on the plates without retreats, the drift loss of E. setigera nymphs increased as the current velocity increased. 4. These results suggested that the habitat amelioration by H. orientalis retreats provided a refuge location for E. setigera nymphs and increased their abundances on stone surfaces exposed to flow forces.     

Status and preliminary mechanism of resistance to insecticides in a field strain of housefly (Musca domestica,L)

Resistance profiles of houseflies (Gol-RR) collected from a field in Golmud city, Qinghai province, China, were determined for seven insecticides using topical bioassays. Resistance ratios of >1219.51, 153.17, >35.43, 6.12, 3.24, 1.73, and 0.86-fold were obtained for propoxur, cypermethrin, imidacloprid, indoxacarb, chlorpyrifos, fipronil, and chlorfenapyr, respectively, relative to a laboratory susceptible strain (SS). Synergism experiments showed that piperonyl butoxide (PBO), triphenylphosphate (TPP), and diethyl maleate (DEM) increased propoxur toxicity by >105.71, >7.88, and >5.15-fold in the Gol-RR strain, compared with 5.25, 2.00, and 1.39-fold in the SS strain, indicating the involvement of P450 monooxygenases, esterases, and glutathione-S-transferase in conferring resistance. Although cypermethrin resistance was significantly suppressed with PBO, TPP, and DEM in the Gol-RR strain, the synergistic potential of these agents to cypermethrin was similar in the SS strain, demonstrating that metabolism-mediated detoxification was not important for conferring resistance to cypermethrin in the Gol-RR strain. However, the three agents did not act synergistically with imidacloprid, indicating that other mechanisms may be responsible for the development of resistance to this insecticide. Acetylcholinesterase (AChE) activity was 13.70-fold higher in the Gol-RR than in the SS strain, suggesting the properties of the AChE enzyme were altered in the Gol-RR strain. Thus, rotation of chlorfenapyr insecticide with other agents acting through a different mode with minimal/no resistance could be an effective resistance management strategy for housefly.     

Functional characterization of the Tetranychus urticae CYP392A11, a cytochrome P450 that hydroxylates the METI acaricides cyenopyrafen and fenpyroximate

Cyenopyrafen is a Mitochondrial Electron Transport Inhibitor (METI) acaricide with a novel mode of action at complex II, which has been recently developed for the control of the spider mite Tetranychus urticae, a pest of eminent importance globally. However, some populations of T. urticae are cross-resistant to this molecule, and cyenopyrafen resistance can be readily selected in the lab. The cytochrome P450s genes CYP392A11 and CYP392A12 have been strongly associated with the phenotype. We expressed the CYP392A11 and the CYP392A12 genes with T. urticae cytochrome P450 reductase (CPR) in Escherichia coli. CYP392A12 was expressed predominately as an inactive form, witnessed by a peak at P420, despite optimization efforts on expression conditions. However, expression of CYP392A11 produced a functional enzyme, with high activity and preference for the substrates Luciferin-ME EGE and ethoxycoumarin. CYP392A11 catalyses the conversion of cyenopyrafen to a hydroxylated analogue (k_cat = 2.37 pmol/min/pmol P450), as well as the hydroxylation of fenpyroximate (k_cat = 1.85 pmol/min/pmol P450). In addition, transgenic expression of CYP392A11 in Drosophila melanogaster, in conjunction with TuCPR, confers significant levels of fenpyroximate resistance.The overexpression of CYP392A11 in multi-resistant T. urticae strains, not previously exposed to cyenopyrafen, which had been indicated by microarray studies, was confirmed by qPCR, and it was correlated with significant levels of cyenopyrafen and fenpyroximate cross-resistance. The implications of our findings for insecticide resistance management strategies are discussed.     

Shading-induced changes in the leaf mesophyll of plants of different functional types

Changes in the structural characteristics of mesophyll induced by shading were investigated in ten species of wild plants of diverse functional types. In all plant types, shading reduced leaf thickness and density by 30–50% and total surface of mesophyll, by 30–70%. The extent and mechanisms of mesophyll structural rearrangement depended on the plant functional type. In the ruderal plants, integral parameters of mesophyll, such as the surface of cells and chloroplasts and mesophyll resistance, changed threefold predominantly because of changes in the dimensions of the cells and chloroplasts. In these plants, shading reduced the volume of chloroplasts by 30%, and the chloroplast numbers per cell declined. The competitor plants showed a twofold increase in mesophyll resistance due to a decrease in the number of photosynthesizing cells per leaf area unit. Moreover, these plants maintained constant dimensions of mesophyll cells, ratios mesophyll surface/mesophyll volume and chloroplast surface/cell surface. In stress-tolerant plants, diffusion resistance of mesophyll remained the same irrespective of the growing conditions, and mesophyll rearrangement was associated with inversely proportional changes in the dimensions of the cells and cell volume per chloroplast. Noteworthy of these plants were relatively constant chloroplasts number per cell, per leaf area unit and total surface area of chloroplasts. The nature of relationship between the mesophyll diffusion resistance and structural parameters of leaf mesophyll differed in plants of diverse functional types.     

Fasciola hepatica demonstrates high levels of genetic diversity,a lack of population structure and high gene flow: possible implications for drug resistance

Fasciola hepatica, the liver fluke, is a trematode parasite of considerable economic importance to the livestock industry and is a re-emerging zoonosis that poses a risk to human health in F. hepatica-endemic areas worldwide. Drug resistance is a substantial threat to the current and future control of F. hepatica, yet little is known about how the biology of the parasite influences the development and spread of resistance. Given that F. hepatica can self-fertilise and therefore inbreed, there is the potential for greater population differentiation and an increased likelihood of recessive alleles, such as drug resistance genes, coming together. This could be compounded by clonal expansion within the snail intermediate host and aggregation of parasites of the same genotype on pasture. Alternatively, widespread movement of animals that typically occurs in the UK could promote high levels of gene flow and prevent population differentiation. We identified clonal parasites with identical multilocus genotypes in 61% of hosts. Despite this, 84% of 1579 adult parasites had unique multilocus genotypes, which supports high levels of genotypic diversity within F. hepatica populations. Our analyses indicate a selfing rate no greater than 2%, suggesting that this diversity is in part due to the propensity for F. hepatica to cross-fertilise. Finally, although we identified high genetic diversity within a given host, there was little evidence for differentiation between populations from different hosts, indicating a single panmictic population. This implies that, once those emerge, anthelmintic resistance genes have the potential to spread rapidly through liver fluke populations.     

Transgenic tobaccos transformed with a gene encoding a truncated form of the coat protein of tomato black ring nepovirus are resistant to viral infection

 Tomato black ring virus (TBRV) belongs to the nepoviruses, an important genus of phytoviruses characterized by isometric particles and by their transmission by longidorid nematodes. As for all other nepoviruses, the coat protein (CP) of TBRV is encoded by the 3′ terminal part of the viral RNA2 (positions 2801–4334). A hybrid gene driving the expression of a truncated form of the TBRV CP was constructed. It contains a frameshift deletion at position T₄₀₆₅ so that in the encoded protein the last 90 amino acids of the wild-type CP are replaced by 52 amino acids encoded by a different reading frame of the viral RNA. This hybrid gene was introduced into the genome of Nicotiana tabacum cv 'Xanthi' plants. When compared to control plants, progeny of some transformants expressing the mutated CP gene (CPm+ plants) showed resistance against TBRV infection. This resistance is characterized by a delay in the appearance of symptoms, a reduction in the number of infected plants and a reduction in virus accumulation. Received: 28 February 1997 / Revision received: 1 August 1997 / Accepted: 24 March 1999     

Functional and immunohistochemical characterization of CCEae3a,a carboxylesterase associated with temephos resistance in the major arbovirus vectors Aedes aegypti and Ae. albopictus

Temephos is a major organophosphate (OP) larvicide that has been used extensively for the control of Aedes albopictus and Aedes aegypti, the major vectors for viral diseases, such as dengue fever, zika and chikungunya. Resistance to temephos has been recently detected and associated with the upregulation of carboxylesterases (CCEs) through gene amplification, in both species. Here, we expressed the CCEae3a genes which showed the most striking up-regulation in resistant Aedes strains, using the baculovirus system. All CCEae3a variants encoded functional enzymes, with high activity and preference for p-nitrophenyl butyrate, a substrate that was shown capable to differentiate temephos resistant from susceptible Aedes larvae. Enzyme kinetic studies showed that CCEae3as from both Ae. aegypti and Ae. albopictus (CCEae3a_aeg and CCEae3a_alb, respectively) strongly interact with temephos oxon and slowly released the OP molecule, indicating a sequestration resistance mechanism. No difference was detected between resistant and susceptible CCEae3a_aeg variants (CCEae3a_aegR and CCEae3a_aegS, respectively), indicating that previously reported polymorphism is unlikely to play a role in temephos resistance. HPLC/MS showed that CCEae3as were able to metabolize temephos oxon to the temephos monoester [(4-hydroxyphenyl) sulfanyl] phenyl O,O-dimethylphosphorothioate. Western blot and immunolocalization studies, based on a specific antibody raised against the CCEae3a_alb showed that the enzyme is expressed at higher levels in resistant insects, primarily in malpighian tubules (MT) and nerve tissues.     

A three amino acid deletion in the transmembrane domain of the nicotinic acetylcholine receptor α6 subunit confers high-level resistance to spinosad in Plutella xylostella

Spinosad is a macrocyclic lactone insecticide that acts primarily at the nicotinic acetylcholine receptors (nAChRs) of target insects. Here we describe evidence that high levels of resistance to spinosad in the diamondback moth (Plutella xylostella) are associated with a three amino acid (3-aa) deletion in the fourth transmembrane domain (TM4) of the nAChR α6 subunit (Pxα6). Following laboratory selection with spinosad, the SZ-SpinR strain of P. xylostella exhibited 940-fold resistance to spinosad. In addition, the selected insect population had 1060-fold cross-resistance to spinetoram but, in contrast, no cross-resistance to abamectin was observed. Genetic analysis indicates that spinosad resistance in SZ-SpinR is inherited as a recessive and autosomal trait, and that the 3-aa deletion (IIA) in TM4 of Pxα6 is tightly linked to spinosad resistance. Because of well-established difficulties in functional expression of cloned insect nAChRs, the analogous resistance-associated deletion mutation was introduced into a prototype nAChR (the cloned human α7 subunit). Two-electrode voltage-clamp recording with wild-type and mutated nAChRs expressed in Xenopus laevis oocytes indicated that the mutation causes a complete loss of agonist activation. In addition, radioligand binding studies indicated that the 3-aa deletion resulted in significantly lower-affinity binding of the extracellular neurotransmitter-binding site. These findings are consistent with the 3-amino acid (IIA) deletion within the transmembrane domain of Pxα6 being responsible for target-site resistance to spinosad in the SZ-SpinR strain of P. xylostella.     

Evolution of resistance to Bt crops: directional selection in structured environments

Abstract Widespread use of transgenic crops that express an insecticidal endotoxin from Bacillus thuringiensis increases the risk of evolution of resistance by the European corn borer and other insect pests. To delay resistance evolution, the high‐dose/refuge strategy is being implemented for Bt maize and Bt cotton. We develop a general modelling framework to understand the invasion and spread of alleles conferring resistance. We show that at least three processes are involved in explaining the effectiveness of the high‐dose/refuge strategy: the intensity of selection, assortative (non‐random) mating due to spatial subdivision, and variation in male mating success also due to spatial subdivision. Understanding these processes leads to a greater range of possible resistance management tactics. For example, efforts to encourage adults to leave their natal fields may have the unwanted effect of speeding rather than slowing resistance evolution. Furthermore, when Bt maize causes high mortality to susceptible target pests, spraying insecticides in refuges to reduce pest populations may not greatly disrupt resistance management.     

Population genetics of the mangrove salt marsh snake, <Emphasis Type="Italic">Nerodia clarkii compressicauda</Emphasis>, in a linear,fragmented habitat

The mangrove salt marsh snake (Nerodia clarkii compressicauda) occupies a unique and disappearing habitat in much of coastal southern Florida. Given extensive habitat fragmentation and high predation pressure in open spaces, it seems likely that populations of N. c. compressicauda consist of isolated groups of related individuals. To assess the degree of population subdivision in this species we genotyped a total of 125 individuals from seven locations along the Florida coast at four microsatellite loci. Overall heterozygosity was moderate (57.7%) and somewhat lower than that seen in other snake species. Population subdivision was particularly pronounced with 19 of 21 sample pair-wise Φ_ST values significantly different from zero and ranging from 0.064 to 0.343 (P ≤ 0.05). About 11 of 39 alleles were private alleles that also tended to be in high frequency in the populations where they occurred (average frequency ~27%). The correlation of genetic and geographic distances was highly significant and positive (r ² = 0.8733 and P < 0.001) with Φ_ST increasing by ~0.01 for every 10 km of separation. Overall, salt marsh snake populations appear to be fractured into isolated neighborhoods on the order of 50–80 km. In spite of its apparent local abundance, we believe that N. c. compressicauda is in need of conservation protection. The combination of extremely low dispersal, narrow habitat requirements, and most importantly, extensive habitat alteration resulting from coastal real estate development may mean that N. c. compressicauda is highly susceptible to population extirpation and potentially extinction.