Using Bayesian state-space models to understand the population dynamics of the dominant malaria vector, Anopheles funestus in rural Tanzania

Background: It is often assumed that the population dynamics of the malaria vector Anopheles funestus, its role in malaria transmission and the way it responds to interventions are similar to the more elaborately characterized An. gambiae. However, An. funestus has several unique ecological features that could generate distinct transmission dynamics and responsiveness to interventions. The objectives of this work were to develop a model which will; 1) reconstruct the population dynamics, survival, and fecundity of wild An. funestus populations in southern Tanzania, 2) quantify impacts of density dependence on the dynamics, and 3) assess seasonal fluctuations in An. funestus demography. Through quantifying the population dynamics of An. funestus, this model will enable analysis of how their stability and response to interventions may different from that of An. gambiae s.l.Methods: A Bayesian State Space Model (SSM) based on mosquito life history was fit to time series data on the abundance of female An. funestus s.s. collected over 2 years in southern Tanzania. Prior values of fitness and demography were incorporated from empirical data on larval development, adult survival and fecundity from laboratory-reared first generation progeny of wild caught An. funestus. The model was structured to allow larval and adult fitness traits to vary seasonally in response to environmental covariates (i.e. temperature and rainfall), and for density dependency in larvae. We measured the effects of density dependence and seasonality through counterfactual examination of model fit with or without these covariates.Results: The model accurately reconstructed the seasonal population dynamics of An. funestus and generated biologically-plausible values of their survival larval, development and fecundity in the wild. This model suggests that An-funestus survival and fecundity annual pattern was highly variable across the year, but did not show consistent seasonal trends either rainfall or temperature. While the model fit was somewhat improved by inclusion of density dependence, this was a relatively minor effect and suggests that this process is not as important for An. funestus as it is for An. gambiae populations.Conclusion: The model's ability to accurately reconstruct the dynamics and demography of An. funestus could potentially be useful in simulating the response of these populations to vector control techniques deployed separately or in combination. The observed and simulated dynamics also suggests that An. funestus could be playing a role in year-round malaria transmission, with any apparent seasonality attributed to other vector species.

Methods for estimating and modelling spruce budworm development rates at constant temperatures

We describe an experimental protocol for measuring the response of spruce budworm postdiapause larval development to temperature. This protocol is specifically designed to include measurements of development near their upper and lower thermal thresholds. The application of this protocol to a laboratory colony allowed for the first experimental evidence that spruce budworm larval development occurs at temperatures as low as 5 °C and as high as 35 °C, and it provides data to fit stage-specific development models. Our protocol is also designed to minimise mortality near the thermal development thresholds, thus allowing for multigenerational studies. We observed developmental plasticity in larvae reared at constant temperatures, particularly the occurrence of up to 42% of some individuals requiring only five instars to complete development compared to the expected six instars. The occurrence exhibited no clear relation to temperature. Although this protocol is specifically designed for spruce budworm, it provides a template for the study of other species’ developmental responses to temperature.

"Heat waves" experienced during larval life have species-specific consequences on life-history traits and sexual development in anuran amphibians

Extreme temperatures during heat waves can induce mass-mortality events, but can also exert sublethal negative effects by compromising life-history traits and derailing sexual development. Ectothermic animals may, however, also benefit from increased temperatures via enhanced physiological performance and the suppression of cold-adapted pathogens. Therefore, it is crucial to address how the intensity and timing of naturally occurring or human-induced heat waves affect life-history traits and sexual development in amphibians, to predict future effects of climate change and to minimise risks arising from the application of elevated temperature in disease mitigation. We raised agile frog (Rana dalmatina) and common toad (Bufo bufo) tadpoles at 19 °C and exposed them to a simulated heat wave of 28 or 30 °C for six days during one of three ontogenetic periods (early, mid or late larval development). In agile frogs, exposure to 30 °C during early larval development increased mortality. Regardless of timing, all heat-treatments delayed metamorphosis, and exposure to 30 °C decreased body mass at metamorphosis. Furthermore, exposure to 30 °C during any period and to 28 °C late in development caused female-to-male sex reversal, skewing sex ratios strongly towards males. In common toads, high temperature only slightly decreased survival and did not influence phenotypic sex ratio, while it reduced metamorph mass and length of larval development. Juvenile body mass measured two months after metamorphosis was not adversely affected by temperature treatments in either species. Our results indicate that heat waves may have devastating effects on amphibian populations, and the severity of these negative consequences, and sensitivity can vary greatly between species and with the timing and intensity of heat. Finally, thermal treatments against cold-adapted pathogens have to be executed with caution, taking into account the thermo-sensitivity of the species and the life stage of animals to be treated.

Neurotransmitters Affect Larval Development by Regulating the Activity of Prothoracicotropic Hormone-Releasing Neurons in Drosophila melanogaster

Ecdysone, an essential insect steroid hormone, promotes larval metamorphosis by coordinating growth and maturation. In Drosophila melanogaster, prothoracicotropic hormone (PTTH)-releasing neurons are considered to be the primary promoting factor in ecdysone biosynthesis. Recently, studies have reported that the regulatory mechanisms of PTTH release in Drosophila larvae are controlled by different neuropeptides, including allatostatin A and corazonin. However, it remains unclear whether neurotransmitters provide input to PTTH neurons and control the metamorphosis in Drosophila larvae. Here, we report that the neurotransmitters acetylcholine (ACh) affect larval development by modulating the activity of PTTH neurons. By downregulating the expression of different subunits of nicotinic ACh receptors in PTTH neurons, pupal volume was significantly increased, whereas pupariation timing was relatively unchanged. We also identified that PTTH neurons were excited by ACh application ex vivo in a dose-dependent manner via ionotropic nicotinic ACh receptors. Moreover, in our Ca2+ imaging experiments, relatively low doses of OA caused increased Ca2+ levels in PTTH neurons, whereas higher doses led to decreased Ca2+ levels. We also demonstrated that a low dose of OA was conveyed through OA β-type receptors. Additionally, our electrophysiological experiments revealed that PTTH neurons produced spontaneous activity in vivo, which provides the possibility of the bidirectional regulation, coming from neurons upstream of PTTH cells in Drosophila larvae. In summary, our findings indicate that several different neurotransmitters are involved in the regulation of larval metamorphosis by altering the activity of PTTH neurons in Drosophila.

Rearing of Bitterling (Rhodeus amarus) Larvae and Fry under Controlled Conditions for the Restitution of Endangered Populations

Among the several dozen European freshwater fish species, only European bitterling (Rhodeus amarus Bloch) and Rhodeus meridionalis belong to the group of ostrakophilous fish. The embryonic and larval development of the fish in this reproductive group until the time of the yolk sac resorption takes place in the gill cavity of river mussels (Anodonta sp. or Unio sp.). This paper presents the results of the European bitterling Rhodeus amarus being reared under controlled conditions. Bitterling larvae were caught together with river mussels in the natural environment and subsequently placed in a tank for behavioural observations. Bitterling larvae were seen swimming in the water within a week of placing the bivalves under controlled conditions. The bitterling larvae were 8.6 ± 0.11 mm long when they started to swim actively. The rearing was conducted in water at 20 and 26 ± 0.5 °C and lasted for 6.5 months (200 days) in both variants. Initially, the larvae were fed with live nauplii of Artemia salina and subsequently with fodder. The bitterlings in tanks with water at 26 ± 0.5 °C were 66.2 ± 3.0 mm long and weighed 3389 ± 548 mg. For comparison, bitterlings kept in water at 20 ± 0.5 °C were 64.48 ± 3.4 mm long and weighed 3242 ± 427 mg. No larval malformities or mortality were observed during the larvae and fry rearing. The bitterlings had well-developed secondary sexual characteristics and exhibited pre-spawning behaviour at the end of the rearing. This produced suitable bitterling stocking material to be used in the conservation of small or endangered populations.

Recruitment, settlement and ontogeny of the serpulid 'Spirobranchus cariniferus' (Gray, 1843)

<p>Serpulids are a globally represented group of polychaetes and can be found in many habitats from the intertidal fringe to the subtidal environment and even in deep-sea ecosystems. These tube-dwelling worms are often described as pioneer species in new or disturbed habitats. Serpulids secrete a calcareous tube and often occur in aggregations. These patches can range from several centimetres to several metres in diameter and may even form reef systems. Accumulations of tube-dwelling worms provide a new habitat for other species and, therefore, serpulids are considered bioengineers. Serpulid aggregations are known to enhance biodiversity and species abundance and may increase water quality through their filter activity. Despite their ecological importance, their ecology and ontogeny have received little attention. Spirobranchus cariniferus, a New Zealand endemic intertidal serpulid, is a substantial contributor to intertidal ecosystems. For this and other Serpulidae, the link between larval development and larval settlement is missing. However, this connection is essential to understand recruitment and ecology of tube-dwelling worms. Therefore, in this thesis, I describe the ontogeny of S. cariniferus from larval development to recruitment and reproduction. In the first data chapter, I present my findings on the recruitment of S. cariniferus in the field. This serpulid settles aggregatively in the field but not necessarily in response to the presence of adult conspecifics, as has been previously reported. Abiotic factors such as sunlight or wave disturbance have a more substantial effect on recruitment rather than the occurrence of adult individuals of the same or a competing species. Additionally, this chapter provides support for the hypothesis that larvae of S. cariniferus may accumulate near the substrate before settlement. Many sessile marine invertebrate taxa occur in either aggregations or as solitary individuals, with potential benefits and disadvantages associated with each configuration. For S. cariniferus, solitary and aggregative individuals can be found in the same habitat. Therefore, the second data chapter compares growth and mortality for individuals living alone or in aggregation. While solitary and aggregative individuals elongate their tubes at a similar rate, further correlations of body to tube sizes lead to the conclusion that solitary worms focus more of their energy on tube length growth rather than body size increment compared to aggregative conspecifics. Mortality is highly variable but does not differ between both configurations. However, individuals living in a patch have a better ability to recover from damage to their tubes. In the last two decades, the idea that gonochorism is the general reproductive pattern for Serpulidae has been challenged, and instead it has been suggested by some that protandry is the more common trait. Therefore, with my third data chapter, I explore maturation and sex ratio of S. cariniferus and whether it changes for individuals living alone vs. in aggregation or based on size. While maturation depends on size, sex does not, and neither maturation nor sex ratio are dependent on whether individuals live in aggregation or not. Further, the ratio of females to males did not favour either sex consistently. For the first time in this species I found evidence of possible hermaphroditism. Through spawning trials and histological sections, I identified nine individuals which simultaneously contained oocytes and sperm cells. I suggest therefore, that S. cariniferus has alternating sexes rather than protandry as a reproductive strategy. In the fourth and final data chapter, I describe the metamorphosis and settlement behaviour of S. cariniferus larvae. For this serpulid species, settlement and metamorphosis are separate and distinct steps that involve both behavioural and morphological changes to the larvae. Further, this entire process can be quite prolonged (i.e. over several days), and at some points can be reversed. It is therefore very important that observations last longer than 24–48 hours, when studying serpulid settlement. As far as I am aware, this is the first study on a serpulid species to examine aggregative settlement in the field in relation to the presence of adult conspecifics and abiotic factors, and also to explicitly test for consequences of solitary vs. group living on growth and mortality. It is also the first to show evidence of hermaphroditism in this species. I hope my research and this thesis stimulates a more inclusive and holistic investigation of serpulids in the future. Larval development, settlement patterns and ontogeny need to be studied in detail if we want to understand the evolution, ecology, impacts and benefits of these and other sessile marine invertebrates.</p>

Recruitment, settlement and ontogeny of the serpulid 'Spirobranchus cariniferus' (Gray, 1843)

<p>Serpulids are a globally represented group of polychaetes and can be found in many habitats from the intertidal fringe to the subtidal environment and even in deep-sea ecosystems. These tube-dwelling worms are often described as pioneer species in new or disturbed habitats. Serpulids secrete a calcareous tube and often occur in aggregations. These patches can range from several centimetres to several metres in diameter and may even form reef systems. Accumulations of tube-dwelling worms provide a new habitat for other species and, therefore, serpulids are considered bioengineers. Serpulid aggregations are known to enhance biodiversity and species abundance and may increase water quality through their filter activity. Despite their ecological importance, their ecology and ontogeny have received little attention. Spirobranchus cariniferus, a New Zealand endemic intertidal serpulid, is a substantial contributor to intertidal ecosystems. For this and other Serpulidae, the link between larval development and larval settlement is missing. However, this connection is essential to understand recruitment and ecology of tube-dwelling worms. Therefore, in this thesis, I describe the ontogeny of S. cariniferus from larval development to recruitment and reproduction. In the first data chapter, I present my findings on the recruitment of S. cariniferus in the field. This serpulid settles aggregatively in the field but not necessarily in response to the presence of adult conspecifics, as has been previously reported. Abiotic factors such as sunlight or wave disturbance have a more substantial effect on recruitment rather than the occurrence of adult individuals of the same or a competing species. Additionally, this chapter provides support for the hypothesis that larvae of S. cariniferus may accumulate near the substrate before settlement. Many sessile marine invertebrate taxa occur in either aggregations or as solitary individuals, with potential benefits and disadvantages associated with each configuration. For S. cariniferus, solitary and aggregative individuals can be found in the same habitat. Therefore, the second data chapter compares growth and mortality for individuals living alone or in aggregation. While solitary and aggregative individuals elongate their tubes at a similar rate, further correlations of body to tube sizes lead to the conclusion that solitary worms focus more of their energy on tube length growth rather than body size increment compared to aggregative conspecifics. Mortality is highly variable but does not differ between both configurations. However, individuals living in a patch have a better ability to recover from damage to their tubes. In the last two decades, the idea that gonochorism is the general reproductive pattern for Serpulidae has been challenged, and instead it has been suggested by some that protandry is the more common trait. Therefore, with my third data chapter, I explore maturation and sex ratio of S. cariniferus and whether it changes for individuals living alone vs. in aggregation or based on size. While maturation depends on size, sex does not, and neither maturation nor sex ratio are dependent on whether individuals live in aggregation or not. Further, the ratio of females to males did not favour either sex consistently. For the first time in this species I found evidence of possible hermaphroditism. Through spawning trials and histological sections, I identified nine individuals which simultaneously contained oocytes and sperm cells. I suggest therefore, that S. cariniferus has alternating sexes rather than protandry as a reproductive strategy. In the fourth and final data chapter, I describe the metamorphosis and settlement behaviour of S. cariniferus larvae. For this serpulid species, settlement and metamorphosis are separate and distinct steps that involve both behavioural and morphological changes to the larvae. Further, this entire process can be quite prolonged (i.e. over several days), and at some points can be reversed. It is therefore very important that observations last longer than 24–48 hours, when studying serpulid settlement. As far as I am aware, this is the first study on a serpulid species to examine aggregative settlement in the field in relation to the presence of adult conspecifics and abiotic factors, and also to explicitly test for consequences of solitary vs. group living on growth and mortality. It is also the first to show evidence of hermaphroditism in this species. I hope my research and this thesis stimulates a more inclusive and holistic investigation of serpulids in the future. Larval development, settlement patterns and ontogeny need to be studied in detail if we want to understand the evolution, ecology, impacts and benefits of these and other sessile marine invertebrates.</p>