Sex in reptiles is determined by genes on sex chromosomes or by incubation temperature. Previously these two modes were thought to be distinct, yet we show that high incubation temperatures reverse ...genotypic males (ZZ) to phenotypic females in a lizard with ZZ and ZW sex chromosomes. Thus, the W chromosome is not necessary for female differentiation. Sex determination is probably via a dosage-sensitive male-determining gene on the Z chromosome that is inactivated by extreme temperatures. Our data invite a novel hypothesis for the evolution of temperature-dependent sex determination (TSD) and suggest that sex chromosomes may exist in many TSD reptiles.
The spatial resources used by a population of lace monitors (Varanus varius) were examined over an active season (September–April) and an inactive season (May–August). In total, 33 monitors were ...observed, of which 23 monitors were radio-tracked for up to 11 months. Radio tracking provided new information on the spatial ecology of V. varius. During summer (December–February), V. varius moved often, over large (184.5 ha) overlapping home-range areas. In the intermediate seasons of spring (September–November) and autumn (March–May), monitors moved less often and used less than 39% of the summer home-range. Finally, in the cold winter season (June–August) many monitors did not move at all and most used less than 5% of their summer home-ranges. The thermal environment, and reproductive status of V. varius affected its use of space, and the importance of these factors varied seasonally. No spatial segregation was noted between monitors, with home-ranges overlapping on average for eight other radio-tracked monitors. The home-range size of V. varius was accurately predicted using published data on body mass and home-range size for the Varanidae.
Environmental flows are a critical tool for addressing ecological degradation of river systems brought about due to increasing demand for limited water resources. The importance of basin scale ...management of environmental flows has long been recognised as necessary if managers are to achieve social, economic and environmental objectives. The challenges in managing environmental flows are now emerging and include the time taken for changes to become manifest, uncertainty around large-scale responses to environmental flows and that most interventions take place at smaller scales. The purpose of this paper is to describe how conceptual models can be used to inform the development, and subsequent evaluation of ecological objectives for environmental flows at the basin scale. Objective setting is the key initial step in environmental flow planning and subsequently provides a foundation for effective adaptive management. We use the implementation of the Basin Plan in Australia’s Murray-Darling Basin (MDB) as an example of the role of conceptual models in the development of environmental flow objectives and subsequent development of intervention monitoring and evaluation, key steps in the adaptive management of environmental flows. The implementation of the Basin Plan was based on the best science available at the time, however, this was focused on ecosystem responses to environmental flows. The monitoring has started to reveal that limitations in our conceptualisation of the basin may reduce the likelihood of achieving of basin scale objectives. One of the strengths of the Basin Plan approach was that it included multiple conceptual models informing environmental flow management. The experience in the MDB suggests that the development of multiple conceptual models at the basin scale will help increase the likelihood that basin-scale objectives will be achieved.
A major outstanding challenge for environmental flow management is to move from a single site, reach or river focus to planning and delivering environmental flows across entire river basins. There is ...a need for case studies of basin‐scale environmental water delivery as a first step in understanding and eventually generalising basin‐scale responses.
The Commonwealth Environmental Water Holder manages a portfolio of water entitlements for protecting and restoring aquatic ecosystems of the Murray–Darling Basin (MDB). This article describes the strategies used by the water holder and the hydrological outcomes of their basin‐scale environmental water delivery program.
There are five delivery strategies used to enhance benefits achieved with available environmental water. Although the volume of commonwealth environmental water is small relative to mean catchment inflows, improvements in baseflows and freshes are seen across the MDB. Water was also successfully delivered into floodplain wetlands.
The case study provides a successful example of implementing a basin‐scale program for environmental water delivery. However, there remains a great need to improve the knowledge, governance and planning tools for managing environmental water for a broad range of ecological demands that operate at the basin‐scale.
We contrasted diets of three turtles (Elseya albagula, Myuchelys latisternum, Emydura krefftii) from free-flowing or impounded rivers in southeastern Queensland, Australia, to evaluate the effects of ...flow regulation. The turtle species encompassed the herbivorous, carnivorous, and omnivorous feeding guilds, respectively. The study design simultaneously considered ontogenetic dietary shifts and seasonal effects on prey availability. Relative to the river samples, diets for three turtles in impoundments were substantially reduced in prey abundance, species richness, and dietary breadth. Turtles with narrower dietary preferences in free-flowing rivers were more affected by dams than was the dietary generalist. For the most omnivorous turtle, qualitative differences were evident in diets from impoundments and rivers; yet considering its greater dietary breadth, quantitative effects on diet were minor. Diets of turtles in impoundments included fewer subaquatic plants and wind fallen fruits than did the diets of turtles in rivers. For the largely carnivorous turtle, fewer aquatic invertebrates were ingested in impoundments than in riverine habitats, and scavenging behavior was noted mainly in impoundments. Multidimensional scaling of the site characteristics identified dams or weirs with back-ups exceeding 20 km as being relatively similar in impacts on prey diversity. Canonical correspondence analysis identified factors of habitat alteration and turtle size as major determinants of underlying variance in the diets. The results suggest that turtle food webs are altered by river regulation. A general finding that turtle diets in impoundments were depleted of aquatic plants or macro-invertebrates pertains to other turtles of conservation importance.
Cooper Creek is one of Australia's largest unregulated river systems and one of the world's most variable large river systems. It is a dynamic environment that oscillates between booms and busts; ...yet, many species thrive in it. One of these species, the Cooper Creek turtle (Emydura macquarii emmotti) has received little attention, despite being one of Australia's largest freshwater turtles and living further inland than any other Australian turtle. We conducted surveys for E. m. emmotti in 2001–2004, 2019, and 2022, focussing predominantly on the Waterloo waterhole. Waterloo had a large population of E. m. emmotti (508 estimated individuals; 95% CI = 447–596) with an estimated density of 64.8 turtles/ha (95% CI = 57.0–76.2) and estimate biomass of 74.4 kg/ha (95% CI = 57.6–100.3 kg/ha). Juveniles were highly abundant in all years, representing up to 63.6% of captured individuals. It was slightly (but not significantly) male‐biased in 2001–2004 and significantly female‐biased in 2019. All sizes and sexes used the floodplain during a flooding event in 2022, but more males than females were captured on the floodplain, and there was evidence of male‐biased dispersal across the years. Compared to Murray River turtles (Emydura macquarii macquarii), E. m. emmotti exhibited megacephaly across all ages and sexes, with particularly pronounced megacephaly in adult females. Algae were present on many individuals (including on the skin and plastron) but was relatively more abundant on juveniles. Leeches were not detected on any of the 66 turtles that were examined for them. The following injuries/malformations were noted: missing or injured limbs (3.2%), missing or injured eyes (1.3%), damaged shells (8.0%), scute/shell anomalies and malformations (10.6%), and marginal scute seams extending into the costals (67.4% of adults, 1.2% of juveniles). This paper presents some of the first work on this unusual turtle and makes recommendations for future research.
•Amphibian populations can re-expand after declines caused by chytridiomycosis.•Expansion of susceptible amphibians can occur despite high disease prevalence.•High quality breeding habitat may buffer ...frog populations against the effects of Bd.•Coarse woody debris has a positive effect on site colonisation.
The disease chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is a key driver of global amphibian declines. While chytridiomycosis can cause extinction, many susceptible species persist after an initial period of decline, albeit with reduced abundance and distribution. Emerging evidence indicates that amphibian abundance can recover within remnant populations, but to date, the capacity of amphibian populations to re-expand into historically occupied habitat has received limited research attention. We surveyed 145 sites in 2011 and 2012 to determine if populations of the whistling tree frog (Litoria verreauxii verreauxii) have re-expanded compared with historical data from 1975–1976, 1990 and 1996. L. v. verreauxii underwent a major range contraction likely caused by chytridiomycosis between the first two time periods. Populations have recently re-expanded, with 39 new sites colonised despite high prevalence of Bd. We suspect that changes in disease dynamics have resulted in the increased coexistence of L. v. verreauxii and Bd. Habitat attributes at sites that retained frogs for the duration of the study indicate that high quality habitat may contribute to buffering against population level effects of Bd. Colonised sites had more coarse woody debris, suggesting a possible habitat management strategy to encourage range expansion for this species. Given sufficient time and adequate source populations in high quality habitat, it is possible that other amphibian species may re-expand from chytridiomycosis-induced declines. This provides an impetus for the protection of historical, but currently unoccupied amphibian habitats and highlights the importance of maintaining high quality habitat to help species survive novel shocks such as pandemic diseases.
Water resources for irrigation in the Murray-Darling Basin have been heavily over-allocated, with major detrimental effects on wetlands and rivers. The Murray-Darling Basin Plan is intended to return ...water from irrigated agriculture to the environment but requires comprehensive, accurate water accounting to achieve this objective. Floodplain harvesting - the diversion and storage of overland flows into on-farm dams - is widely practised by irrigators in the northern Basin. By reducing volumes of river flows, floodplain harvesting has negative effects on downstream water users and the environment. The volume of diversions is not known, creating a major source of uncertainty over water availability and use. We focussed on floodplain harvesting in northern New South Wales (NSW) catchments (Border Rivers, Gwydir, Namoi, Macquarie and Barwon-Darling) because the NSW government is attempting to licence and regulate the practice. We found in 2019-20 there were 1,833 storages in these catchments with a total surface area of 42,650 ha. Storage capacity has risen from 557 GL in 1993-94 to 1,067 in 1999-2000, 1,225 in 2008-09 to 1,393 GL in 2019-20, a 2.5-fold increase in 26 years. We estimated mean annual floodplain harvesting take (2004-2020) in northern NSW was 778 GL (range 632-926 GL). For context, this volume represents half of the mean volume of held environmental water released annually for the entire Basin between 2009-10 and 2018-19 (1,576 GL) and six times that for the northern NSW Basin (125 GL). The volume of take from floodplain harvesting is not sustainable and in breach of legislation on water use and management. We discuss the negative impacts of floodplain harvesting on downstream communities and flow-dependent ecosystems and their social justice implications.
The Murray–Darling Basin in south‐eastern Australia contains over 70,000 km2 of wetlands and floodplains, many of which are in poor condition. In response, Australian governments have committed to a ...major restoration program, the Murray–Darling Basin Plan that includes management of 2,750 Gl of environmental water to protect and restore aquatic ecosystems. The restoration is being undertaken within an adaptive management framework that includes monitoring the outcomes of environmental flows in seven river valleys. This paper provides an overview of the 5‐year monitoring project and some preliminary results. Monitoring design considered the Basin Plan's environmental objectives, conceptual models of ecosystem responses to flow, and an outcomes framework linking flow responses to the environmental objectives. Monitoring indicators includes ecosystem type, vegetation, river metabolism, and fish. Responses are evaluated to identify the contribution of environmental flows to Basin Plan environmental objectives and continual improvements in management. The program is unique in that it seeks to monitor long‐term outcomes of environmental flows at the river basin scale. Despite many challenges, the monitoring has become a key part of the adaptive management of environmental flows in the Murray–Darling Basin.
Varanus rosenbergi females oviposit in nests excavated in termite mounds in summer, and hatching occurs the following spring after a seven-month incubation period. In this study, we characterized ...developmental features associated with the prolonged incubation of this species at Kangaroo Island in South Australia. Oviposition occurs shortly after limb buds have formed, and the subsequent pattern of organogenesis is similar to that of other lizards. Survival of eggs incubated at constant temperatures ranging from 26–33°C was 89–100%, whereas survival at 24°C and at 35°C was 0 and 14%, respectively. During the incubation period, mean ambient temperature at Kangaroo Island (14–15°C) is too low for successful reproduction, whereas mean temperatures in termite mounds (27–37°C) are substantially warmer and similar to the estimated mean incubation temperature (26–27°C). Therefore, successful reproduction by V. rosenbergi in southern Australia may be contingent on nesting in termitaria. Varanids, in general, have incubation lengths that are substantially longer than those of most other squamates, turtles, and crocodilians. We hypothesize that varanids have prolonged incubation lengths primarily as an adaptation to maximize hatchling fitness because their emergence from nests in the warm and/or wet season of the year following oviposition is the time most favorable for growth and survival. Other factors that may contribute to prolonged incubation are the developmental costs of a large brain and the energy costs associated with nest locations and substrates that may make emergence difficult for hatchlings.
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