Proportion Of Hatchlings Research Articles

Modeling the impacts of temperature during nesting seasons on Loggerhead (Caretta caretta) Sea Turtle populations in South Florida

Loggerhead sea turtles (Caretta caretta) are a threatened sea turtle species that nests on beaches along the northwestern Atlantic Ocean. Loggerhead nesting in Florida accounts for approximately 80% of the loggerhead population in the Atlantic Ocean, yet the underlying ecological mechanisms behind their population dynamics are understudied. C. caretta are largely inaccessible since they spend most of their early life in open ocean habitats. Consequently, their nesting and hatchling production offer quantifiable insight of their population dynamics. Emergence success, the proportion of eggs laid that produce offspring which successfully leave the nest, is the source of all later life stages. Yet the abiotic factors that drive emergence success trends have not been fully described. This study explores the relationship between air temperature and emergence success across multiple nesting seasons to better understand the potential impact of anthropogenic climate change on subsequent loggerhead populations. Here we investigate the effect of changing emergence success on the juvenile and adult life stages. After exploring numerous aspects of temperature and precipitation metrics, we determined that the mean of the maximum daily temperatures for each trimester of the eggs’ incubation periods related most closely to the variation in emergence success (the proportion of hatchlings that make it out of the nest) across nests. A novel feature of our approach to modeling the impact of temperature on the later life stages is through connecting a statistical model into a discrete mechanistic population model. Our population model has two parts, one with eggs and hatchlings on a daily time scale in the nesting season and the other with juveniles and adults on an annual time scale. The statistical model enables us to illustrate the effect of temperature changes across these life stages. The decline in the adult population follows from the decline of the hatchling emergence success. Using predicted increases in temperature due to climate change, we illustrate a corresponding prediction for the population classes.

Behavioral Variability of Hatchlings Modifies Dispersal Potential in Crown Conch (Melongena corona): Why Do Larvae Crawl Away but Sometimes Swim?

AbstractThe diversity and consequences of development in marine invertebrates have, for a long time, provided the opportunity to understand different evolutionary solutions to living in variable environments. However, discrete classifications of development can impede a full understanding of adaptation to variable environments when behavioral, morphological, or physiological flexibility and variation exist within traditionally defined modes of development. We report here novel behavioral variability in hatchlings of a marine gastropod, the Florida crown conch (Melongena corona), that has broad significance for understanding the correlated evolution of development, dispersal, and reproductive strategies in variable environments. All hatchlings crawl away from egg capsules after emergence as larval pediveligers. Some subsequently swim for a brief period (seconds to minutes) before crawling again. From detailed observations of 120 individuals over 30 days, we observed 28 (23.3%) hatchlings swimming at least once (8%-50% per maternal brood). The propensity to swim was unrelated to time spent encapsulated or size at hatching and lasted for 22 days. We manipulated hypothesized environmental cues and found that the proportion of hatchlings that swam was highest in the absence of cues related to habitat or juvenile food and lowest when only habitat cues were present. The relative growth rate of hatchlings was highest when habitats contained a putative juvenile food source. About 44% of hatchlings were competent to metamorphose at emergence but did not metamorphose at this time in the lab or the field. The rate of metamorphosis increased with age and depended on the presence of unknown cues in the field. Crawl-away larvae with prolonged swimming ability may be an adaptation to balance the unpredictable risks of exclusively benthic or pelagic development and to allow the option to disperse to higher-quality habitat.

Range Limits and Demography of a Mountaintop Endemic Salamander and Its Widespread Competitor

Range limits can be caused by a multitude of abiotic or biotic factors, but all of these must act through the demography of range-edge populations. Woodland salamanders of the genus Plethodon often exhibit distinct range boundaries where the distributions of competing species meet. Because of their high densities and low mobility, Plethodon are well suited for studies of how fitness-related traits change as species approach their range limits. Across contact zones between the mountaintop endemic Peaks of Otter Salamander (Plethodon hubrichti) and the widespread Eastern Redback Salamander (Plethodon cinereus), we measured changes in three salamander traits: 1) body condition, 2) frequency of tail loss, and 3) proportion of hatchlings. We then used hierarchical Bayesian models to compare these traits among five site types: allopatric sites for both species, sites where one of the species was dominant and the other was rare, and mixed sites containing high densities of both species. For P. hubrichti, we found no consistent changes in body condition across contact zones. However, frequency of tail loss increased continuously from allopatric sites (21%) to rare sites (54%). We also found evidence of reduced hatchling proportions at sites outside of allopatric areas (15–16% versus 30% at allopatric sites). For P. cinereus, body condition was higher at allopatric sites compared to sites within the contact zone. Similar to P. hubrichti, frequency of tail loss in P. cinereus increased continuously from allopatric sites (27%) to sites where P. cinereus were rare (50%). However, for P. cinereus, we did not find evidence of reduced hatchling numbers towards the edge of their range margin. Overall, our results suggest that both species likely have reduced fitness as they approach their range margin. Tail loss, which may reflect interference competition, effects of predation, or interactions between these, could potentially act as a density-dependent factor that stabilizes the range boundary between these species, at least over shorter time scales.

Plumage color and reproductive output of eastern bluebirds (Sialia sialis) nesting near a mercury-contaminated river

Despite the growing evidence of mercury's impact on ecosystems, few studies have looked at the environmental impact of mercury pollution on terrestrial songbirds and the complex ways through which mercury might influence their fitness. In 2007–2008 eastern bluebirds (Sialia sialis) were monitored on mercury contaminated and reference sites for blood and feather mercury, reproductive success and plumage coloration. Higher tissue mercury accumulation was associated with plumage that was overall brighter and shifted towards the UV portion of the spectrum. In females, long-term mercury exposure, as indicated by feather mercury, was associated with smaller clutches of eggs. In males, recent mercury exposure, as indicated by blood mercury, was associated with a reduction in the proportion of hatchlings that fledged, potentially through reduced male provisioning of offspring. Reproductive success and plumage color are closely linked in bluebirds through mate choice, and our findings indicate that mercury contamination is associated with reproductive success directly and possibly indirectly, through coloration of bluebirds.

A Comparison of Hatchling Locomotor Performance and Scute Pattern Variation between Two Rookeries of the Flatback Turtle (Natator depressus)

Marine turtle species consist of several genetically discrete ‘evolutionarily significant units’ (ESUs) which do not interbreed. We studied Flatback turtle (Natator depressus) hatchlings from two rookeries (Mon Repos Conservation Park and Bare Sand Island, Australia) representing two separate ESUs. Turtles from these ESUs differ in several key life history traits, including body size, and we predicted hatchlings would also differ in locomotor performance. We also investigated the proportion of hatchlings with non-modal scute patterns to determine whether this varies between ESUs. We collected newly emerged hatchlings, and measured mass, carapace length and width, and recorded the scute pattern. We then measured self-righting ability and crawling speed. Our results confirmed a difference in hatchling size between the two ESUs, with Mon Repos rookery hatchlings being larger. However the size difference did not translate into a difference in self-righting ability or crawling speed. The Mon Repos rookery also produced a larger proportion of hatchlings with major non-modal scute pattern compared to Bare Sand Island rookery. The differences suggest hatchling survival rates may differ between ESUs, and that ESUs should be studied separately when implementing conservation measures.

Effects of Beach Renourishment and Clutch Relocation on the Success of the Loggerhead Sea Turtle (Caretta caretta) Eggs and Hatchlings

Along the coasts of Florida, beach erosion caused by large storms and hurricanes coincides with the nesting season of the Loggerhead Sea Turtle. Here, we report the effects of beach renourishment and nest relocation on the success of Loggerhead Sea Turtle (Caretta caretta) eggs and hatchlings. Data on ∼53,700 Loggerhead Sea Turtle eggs from 517 clutches were collected over a six-year period, 2006 through 2011, on the Gulf Coast beaches of Pinellas County, Florida. We compared the proportion of eggs that hatched and hatchlings that emerged based on relocation; the type of beach on which breeders deposited their eggs (natural or renourished), and the type of beach to which clutches were relocated (natural or renourished). In this study, beach renourishment had no adverse effect on the proportion of eggs that hatched or the proportion of hatchlings that emerged. In contrast, clutch relocation decreased the proportion of inundated clutches 10-fold from 28–3%; an important finding as water inundation destroyed nearly half of the eggs per clutch. These findings add to a growing body of research on beach renourishment and clutch relocation with important implications for the continued management of Loggerhead Sea Turtle nests.

Effects of Temperature on Hatching Time and Hatchling Proportions in a Poecilogonous Population of Haminoea zelandiae

Poecilogony is a relatively uncommon life-history strategy that results in the production of two different larval forms from the same egg mass (e.g., free-swimming lecithotrophic larvae and post-metamorphic, crawling juveniles). In this study, a population of the opisthobranch gastropod Haminoea zelandiae from Pauatahanui Inlet, New Zealand, was found to exhibit poecilogony. Further, differences in development, hatching times and proportion of hatchlings that were veligers or juveniles were examined for egg masses in two temperature regimes in the laboratory: cool (15-17 °C), and warm (21-23 °C). Hatching proportions were also examined for egg masses collected from the field (where temperatures ranged from 21-23 °C) for varying lengths of time (1 d, 5 d, and 10 d post-spawning). Hatchlings from egg masses in warmer temperatures developed faster and hatched earlier than those in cool temperatures. In the laboratory, egg masses in warm conditions hatched a greater proportion of post-metamorphic juveniles (45.4%) compared to egg masses in cool conditions (24.6%) Further, egg masses that had been in the field 10 d before hatching (i.e., more days at warmer temperatures) exhibited a greater proportion of post-metamorphic juveniles (67.9%) than those that were collected after only 1 d in the field (25.1%). Together these results suggest that temperature may have an important role in mediating dispersal strategies in this poecilogonous species.

Postnatal effects of incubation length in mallard and pheasant chicks

Eggs of mallard ducks (Anas platyrhynchos) and ring‐necked pheasants (Phasianus colchicus) were incubated in clutches arranged to stimulate embryos to hatch earlier or later than normal. This manipulation of hatching time was achieved by combining eggs of different age in the same clutch. To ensure hatching synchrony, embryos communicate with each other during the last stage of incubation, resulting in either a delay or an acceleration of hatching. Embryos of both species that accelerated their hatching time suffered a higher mortality rate after hatching. Combining mortality with the proportion of hatchlings that suffered from leg deformities, impeding their movements, resulted in a cost also to pheasant chicks delaying their hatching. Chicks of both species accelerating hatching time had a lower minimum mass and a shorter tarsus length than control chicks, whereas chicks delaying hatching time either grew as well or slightly better than control chicks. Mallard chicks had better balance and mobility immediately after hatching the longer they stayed in the egg. This indicates that the period immediately before hatching, is an important period for muscular and organ maturity. Reducing this period results in costs affecting post‐hatching survival. The strategy to assure synchronous hatching in mallards and pheasants probably reflect a trade‐off between the negative effects of shifting the age at hatching away from normal and differences in predation risk during different stages of reproduction.

Alarm response of hatchlings of the apple snail, Pomacea canaliculata (Gastropoda: Ampullariidae), to aqueous extracts of other individuals

We examined how hatchlings of the freshwater snail, Pomacea canaliculata, responded to aqueous extracts of conspecific hatchlings. Three, 3‐day‐old hatchlings were macerated in deionized water (1 mg hatchling per 1 ml water). When 0.5 ml of the aqueous extract was added to a test tube containing 10 hatchlings of the same age and 50 ml of water, the hatchlings in the water began to crawl out of the water within 5 min. The proportion of hatchlings that crawled out of the water approached 0.6–0.9 after 1 h, but gradually decreased to 0.4 after 24 h. The relatedness between the live and the macerated hatchlings had no significant influence on the response. Hatchlings of egg masses obtained either in the laboratory or in the wild responded similarly to aqueous extracts of hatchlings from either egg mass. This suggests that the conditions under which the egg masses were incubated or the conditions that their parents had experienced had no effect on the hatchlings’ response. When compared with experiments reported on other aquatic animals, we consider the behavior of the hatchlings to be an alarm response of escaping from predators.

Relative contributions of organochlorine contaminants, parasitism, and predation to reproductive success of eastern spiny softshell turtles (Apalone spiniferus spiniferus) from southern Ontario, Canada.

We examined hatching success, predation rates, rates of parasitism, sex ratio, and egg viability in eggs of the eastern spiny softshell (Apalone spiniferus spiniferus), a threatened species in Canada. Eggs were monitored from three populations, located at Thames River, Rondeau Provincial Park, and the Long Point National Wildlife Area, in southern Ontario, Canada in 1998. Concurrently, we measured organochlorine pesticides, PCBs, dibenzo-p-dioxins and furans from eggs from the same nests. Contaminant concentrations in eggs were similar among sites. There was no correlation between hatching success, parasitism and depredation rates, or the proportion of hatchlings that were males with total PCBs or individual pesticides, but there was a positive correlation between egg viability with concentrations in eggs of total PCBs, and with five pesticides. We found no evidence that the reproductive success of softshell turtles was compromised due to organochlorine contamination. The most important factors determining hatching success of eggs was predation, followed by egg viability and parasitism.

Effect of Feathers as Nest Insulation on Incubation Behavior and Reproductive Performance of Tree Swallows (Tachycineta bicolor)

-Many species of birds line their nests with feathers, presumably because of the insulative qualities of feathers and because feathers may act as a barrier between nest parasites and nestlings. In 1993, we experimentally examined the role of feathers as nest insulation on the incubation behavior, nestling growth, and reproductive performance of Tree Swallows (Tachycineta bicolor) nesting in boxes in western Michigan. There were no significant differences between the incubation rhythms of females with experimental nests (i.e. no feathers) and females with control nests (i.e. with feathers). Nestlings that were reared in control nests had significantly longer right tarsi and right wing chords; their masses were significantly greater than nestlings reared in experimental nests. In addition, nested analyses of variance indicated that both female age class (i.e. second year, after second year, or after hatching year) and the brood within which a nestling was reared had significant effects on nestling growth until nestling day 12. Whether an individual nestling was infected with ectoparasites was independent of whether it was reared in an experimental or control nest. Nest insulation affected reproductive performance: females with experimental nests had significantly longer incubation periods and produced significantly fewer fledglings than did females with control nests. These results suggest that nest insulation may be an important factor influencing incubation behavior, nestling growth, and reproductive performance of Tree Swallows in western Michigan. Received 21 November 1994, accepted 21 June 1995. NESTS ARE an important component of parental effort in birds. Nests provide safety from predators, and a container and microenvironment for incubating parents, developing eggs, and nestlings (Collias and Collias 1984). Nest building is influenced by instinct and learning: the nests of experienced birds often are superior to those built by novices (Collias and Collias 1984). Determining the consequences of individual differences in nest architecture on reproductive performance are important to a complete understanding of the factors affecting the evolution of parental effort in birds. Tree Swallows (Tachycineta bicolor) build nests made of a mat of dry grasses with a nest cup lined with feathers. Females do most of the nest building (Kuerzi 1941, Sheppard 1977), but males add many of the feathers that line the cup (Sheppard 1977, Cohen 1985). The nests of second-year females are less well feathered than nests built by after-second-year females (Lombardo 1994). Differences in nest feathering may influence the age-related differences in reproductive performance that have been observed in Tree Swallows (DeSteven 1978, 1980, Stutchbury and Robertson 1988) because of the effects of feathers on the thermoenergetics of incubation, brooding, and nestling growth. Winkler (1993) experimentally examined the effect of feathers as nest insulation on reproductive performance in Tree Swallows nesting in boxes near Ithaca, New York, and found that feathers as nest lining had no effect on fledging success, but nestlings reared in control nests (i.e. with feathers) were larger on the twelfth nestling day, fledged earlier, and had fewer ectoparasites than those reared in experimental nests (i.e. without feathers). He did not examine whether there were female age-related differences in reproductive performance that were influenced by feathers as nest insulation. Lombardo (1994) did a correlational study of nest architecture, female age, and reproductive performance of Tree Swallows nesting in southeastern Michigan and found no relationship between the amount of nest feathering and the number or proportion of hatchlings and fledglings produced. However, well-insulated nests were advantageous early in the season when ambient temperatures were low and eggs and nestlings needed to be kept warm, but disadvantageous late in the season when ambient