ASSORTATIVE MATING AND NATURAL SELECTION IN AN IRIS HYBRID ZONE

The phenology of different genotypes and the distribution of genetic variation among flowering plants and their progeny were examined to assess the levels of assortative mating and selection in a hybrid population of Iris. This study and a previous survey of RAPD nuclear markers and chloroplast markers indicate that the population consists of parental genotypes and recombinant hybrid genotypes that are similar to the parental species (I. fulva and I. brevicaulis), although lacking intermediate genotypes. Early in the season only I. fulva genotypes produced flowers, but as flowering in these plants decreased, the hybrid genotypes and I. brevicaulis genotypes began flowering, resulting in a 24-d period of coincidental flowering. The genotypic distribution of seeds produced during the period of flowering overlap contained a high frequency of intermediate genotypes that were not present in the adult generation. The degree of effective assortative mating was examined by comparing the observed progeny genotypic distributions with expected distributions from a mixed-mating model. The model included selfing and random outcrossing to the nearest plants that had pollen-bearing flowers on the day the recipient flower was receptive. The observed genotypic distribution of progeny from plants with I. brevicaulis chloroplast DNA (cpDNA) was not significantly different from the expected distribution. For I. fulva genotypes, however, there were higher than expected frequencies in the extreme genotypic classes, although intermediate genotypes were absent, indicating that these plants were preferentially mating with similar genotypes. Compared with the extreme genotypes, a larger proportion of the intermediate seed progeny produced were aborted, indicating that intermediate genotypes have lower viability. On the basis of the observed progeny genotypes and genetic disequilibria estimates for the adults and the progeny, there appears to be a pattern of effective asymmetrical mating in this population. This asymmetry is most likely due to pollen-style interactions that reduce the fertilization ability of genetically dissimilar pollen, or preferential abortion of genetically intermediate zygotes by I. fulva-like genotypes. The lack of any apparent discrimination by I. brevicaulis-like genotypes creates a directional exchange of nuclear genetic elements that will have implications for introgression and the evolution of hybrid genotypes.     

Hydrologic,vegetation, and substrate characteristics of floating marshes in sediment-rich wetlands of the Mississippi river delta plain,Louisiana, USA

Floating marshes occur over 70% of the western Terrebonne Basin, Louisiana, USA, freshwater coastal wetlands. They are of several types: A free-floating thick-mat (45–60 cm) marsh dominated by Panicum hemitomon and Sagittaria lancifolia; a thick mat marsh dominated by Panicum hemitomon and Sagittaria lancifolia that floats part of the year, but whose vertical floating range is damped compared to adjacent water; and an irregularly-floating thin mat (< 30 cm) dominated by Eleocharis spp. in the spring and Ludwigia leptocarpa and Bidens laevis in the summer and fall. Floating mats must be almost entirely organic in order to be buoyant enough to float. The western Terrebonne wetlands receive large winter/spring supplies of suspended sediments from the Atchafalaya River. Even though sediment concentrations in the adjacent bayou are as high as 100 mg l^–1, the Panicum hemitomon/Sagittaria lancifolia free-floating marsh probably receives no over-surface sediments since it floats continuously. The bulk density data of the damped-floating marsh, however, suggest some mineral sediment input, probably during winter when this marsh is submerged. These two types of floating marsh could not have developed in the present sediment regime of the Atchafalaya River, but as long as they remain floating can continue to exist. Thin floating mats are found in areas receiving the least sediment (<20 mg 1^–1 suspended sediment concentration in adjacent bayous). This low sediment environment probably made possible their formation within the past 20 years. They may represent a transitional stage in mat succession from (1) existing thick-mat floating marsh to a degrading floating marsh, or (2) a floating marsh developing in shallow open water.Corresponding editor: D. Whigham     

Luteal function in the hysterectomized bitch following treatment with prostaglandin F2α (PGF2α)

Estrus and ovulation were induced in ten mature, mixed-breed, anestrous bitches (10 to 20 kg) using exogenous gonadotropins. Bitches were bred once, on the second day of estrus. Between 11 and 13 days following estrus, bitches were bilaterally hysterectomized and randomly divided into two treatment groups of five bitches each. Four days following surgery, Group A (treated) was given a single subcutaneous injection of PGF₂α (Prostin F₂ alpha^®) at a dose of 1 mg/kg body weight and Group B (controls) similarly given an equal volume of .9% saline. Blood samples were collected daily by cephalic venipuncture prior to surgery and for 75 days thereafter. Plasma progesterone was monitored by a radioimmunoassay method. Although bitches were teased daily following PGF₂α or saline treatments, estrual behavior was not exhibited. In both the PGF₂α and saline treatment groups, plasma progesterone levels showed a transient decline by 12 hours following injection, although a more dramatic decrease was observed at this time in the prostaglandin-treated bitches. Subsequently, progesterone concentrations tended to increase in both groups at 6 days following treatment, however, not to pre-treatment levels. Within 20 to 32 days following treatment in both groups, plasma progesterone levels declined to <1 ng/ml and remained depressed at least 60 days post-injection. In this study, complete luteal regression was not induced following PGF₂α treatment. Luteal function in both groups, as indicated by plasma progesterone concentrations, was shortened in the absence of the uterus.     

Evaluation of Effects of Harvest on Alligator Populations in Louisiana

Biologists with the Louisiana Department of Wildlife and Fisheries, Louisiana, USA, have managed statewide annual harvest of alligators (Alligator mississippiensis) for 35 years (1981–present). We collected and analyzed harvest data for Louisiana alligators to determine the effects of harvest on the population structure, focusing on the larger size classes (≥274 cm) of this slow-growing species. Linear regression analyses revealed that body size-class structure, based on overall average size and the percentage of animals harvested in the larger size classes was relatively stable. Annual aerial alligator nest counts indicated a continual growth of the population, and over time harvested alligators maintained a constant average size. Analyses of population size (based on number of nests and population modeling) indicated that the current annual harvest represents approximately 3% of the population. Linear regression analysis showed that annual hunter success declined only slightly during the study period, and the scheduling of the hunt season after the hatch period and recommended hunting in areas not frequented by breeding females provides economic opportunities for hunters to participate in a sustainable harvest that preserves the larger size classes of alligators in the population. Strict enforcement of existing laws was a key factor responsible for the success of this harvest program. Comparison of alligator population size and number of harvest-related citations indicated that illegal harvest did not have a negative effect on population size, and linear regression analyses revealed that the rate of increase in citations was lower than the increase in populations over the study period. The results of this harvest program indicated that alligators can be hunted in a sustainable manner if hunting is conducted after the hatch period and occurs in areas that primarily exclude the harvest of adult females, and strict law enforcement curbs illegal activities that negatively affect populations. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.     

GENETIC INTERACTIONS AND NATURAL SELECTION IN LOUISIANA IRIS HYBRIDS

Hybridization between divergent lineages has long been assumed to give rise to unfavorable interactions between the parental genomes. These deleterious genetic interactions are further assumed to result in the production of hybrid offspring with decreased levels of viability and/or fertility. To test this assumption, we investigated the role of both nuclear and cytonuclear epistatic interactions in determining the frequencies of F₂ genotypes produced in crosses between two species of Louisiana iris, Iris fulva and I. brevicaulis. Overall, these crosses revealed a significant deficit of intermediate hybrid genotypes accompanied by an excess of parental-like genotypes, suggesting that genetic interactions may promote postmating reproductive isolation between these species. However, analyses of single and multilocus segregation patterns revealed a variety of negative and positive interactions between the genomes of the parental taxa at the nuclear and cytonuclear levels. Taken together, these results indicate that the traditional view that interactions between divergent genomes are always deleterious is an oversimplification. Rather, it seems likely that crosses between divergent lineages can lead to the production of both fit and unfit hybrid genotypes.     

Space Use and Habitat Selection by Female Louisiana Black Bears in the Tensas River Basin of Louisiana

Abstract: Studies of space use and habitat selection of endangered species are useful for identifying factors that influence fitness of individuals and viability of populations. However, there is a lack of published information regarding these behaviors for the federally threatened Louisiana black bear (Ursus americanus luteolus). We documented space use and habitat selection for 28 female black bears in 2 subpopulations of the Tensas River Basin population in northeast Louisiana, USA. The Tensas subpopulation inhabits a relatively large (>300-km²) contiguous area of bottomland hardwood forest, whereas the Deltic subpopulation exists mainly in 2 small (<7-km²) forested patches surrounded by an agricultural matrix. Females on Deltic maintained smaller seasonal and annual home ranges than females on Tensas (all P < 0.04), except for females with cubs during spring. On Tensas, females with cubs maintained smaller home ranges than females without cubs during spring (P = 0.01), but we did not detect this difference on Deltic or in other seasons. Females on Tensas and Deltic exhibited differences in habitat selection when establishing home ranges and within home ranges (P < 0.001). Deltic females selected mature bottomland hardwood forests and avoided agricultural habitats at both spatial scales. Tensas females selected a mixture of swamps, mature and regenerating forests, and exhibited variation in selection across scale, season, and reproductive status. We suggest that differences in space use and habitat selection between Tensas and Deltic are at least partially due to habitat differences at the landscape (i.e., amount of forested habitat) and patch (i.e., food availability) scales. Our results contribute to the understanding of factors that influence space use and habitat selection by black bears and provide specific information on habitat types selected by Louisiana black bears to agencies involved in habitat protection and restoration for this threatened subspecies.     

Temporal variation and landcover influence survival in adult female mottled ducks

Adult survival is a key driver of waterfowl population growth and is subject to temporal and spatial variation. Mottled ducks (Anas fulvigula) are native to the Gulf Coast and peninsular Florida, USA, and have suffered population declines over the past decade, especially in Texas and Louisiana, USA. Although the cause of this decline is not well understood, previous research concluded variation in survival contributed to nearly a third of variation in the species' population growth rate. We used global positioning system-groupe spécial mobile (GPS-GSM) transmitters to study temporal and spatial variation in survival of adult female western Gulf Coast mottled ducks in southwestern Louisiana, 2017–2020. We evaluated weekly survival models parameterized with combinations of hunted and non-hunted periods, biological seasons, and landcover types that were used by mottled ducks. There were 3 competitive survival models, and all contained 4 parameters that parsed the annual cycle into the non-hunted period, first part of the general waterfowl season, and second part of the waterfowl season, and included the proportion of GPS locations in agricultural lands. Weekly survival was 0.979 during the first part of the general waterfowl hunting season, and 0.996 during the second part of the general waterfowl season. Daily survival rate increased with an increasing proportion of locations logged in agricultural lands. Annual survival rates were similar to other waterfowl that are not experiencing population declines, which suggests survival is not limiting population growth of mottled ducks along the western Gulf Coast. Managers should ensure the availability of refuge areas where hunting is prohibited during the first part of the general waterfowl season, when mottled ducks are at an increased risk of mortality, in addition to the targeted conservation of agricultural lands that provide cover and forage.     

The Nearctic-Caribbean species Leptotrachelus dorsalis (Fabricius, 1801): Larval descriptions with a diagnosis of immature Ctenodactylini and natural history notes on the genus and tribe (Coleoptera, Carabidae)

Adults and larvae of Leptotrachelus dorsalis (Fabricius), the Sugarcane Savior Beetle, live in association with grasses, the larvae in the appressed leaf axils. Both adult and larval Leptotrachelus dorsalis eat larvae of the Sugarcane Borer, Diatraea saccharalis (Fabricius), and perhaps other insects living in the confines of the leaf sheaths of that and other grass-like species. The geographic range of Leptotrachelus dorsalis extends from Kansas in the west to the Atlantic seaboard, north as far as Ontario, Canada and south to Cuba; it is an eastern species of North America and the Caribbean. Larval character attributes that are shared with a related ctenodactyline, Askalaphium depressum (Bates), provide a preliminary basis for characterization of the immatures of tribe Ctenodactylini.