Does Size Matter? The Case of the Courtship Pyramids in Red Sea Ghost Crabs (Ocypode saratan)

Display, wherein males attempt to maximize fitness by attracting sexually mature females to mate, is known to drive speciation by Sexual Selection. We researched the Red Sea Ghost Crab (Ocypode saratan; RSGC), in which males build display pyramids to attract females. The study was conducted at the beach in Eilat, Israel. At each session, we measured the height (in cm) of all pyramids and the dimensions (height, breadth; in cm) of the burrow entrance. We assumed that the size of the entrance represented the relative size of the carapace width of the occupant. The mean (± SE) entrance volume was 230.8 ± 11.7 cm, and the height of the pyramid was 11.8 ± 0.49 cm (n = 54). The results of our study did not support our hypothesis because we had expected to find a linear correlation between body size and pyramid height, i.e., the larger the male, the larger the pyramid. However, our results show that the largest males in the population either built small pyramids or not at all, and the cut-off of the larger crab’s body size appears to be around 350 cm3. We discovered a step-wise function in the data in that crabs with the smallest body size of ca. 250 cm3 constructed the highest pyramids, with a declining tendency between 250–350 cm3 and extremely low pyramids beyond 350 cm3. However, our findings need to be further studied with a stress on the ambiance and elucidate whether the habitats differ in temperature, humidity, prey-base, etc., before concluding as to why the larger males desist from building pyramids. This study underwrites the importance of studying the mating systems of the macro-fauna of the beaches that are fast disappearing owing to anthropogenic development.

Individual Laterality in Ghost Crabs (Ocypode saratan) Influences Burrowing Behavior

Behavioral handedness is known to enhance an individual’s handling capabilities. However, the ecological advantages in brachyuran crustaceans remain unclear, despite the Ocypode species having been studied extensively. Thus, in this study, we analyzed the laterality of the endemic Red Sea ghost crab on one beach in Eilat, Israel. We successfully documented the laterality of the large cheliped in 125 crabs; in 60 (48.0%), the right cheliped was larger, and in 64 (51.2%), the left. We also observed temporal segregation between the right- and left-clawed crabs. The right-handed crabs start activity just after sunrise, while left-handed crabs appear ca. 40 min after it. Similarly, temporal segregations were also observed in the evening. The right-clawed crab activity peaked ca. 20 min before sunset, while the left-clawed crabs were active uniformly. Additionally, burrow entrances corresponded to the larger cheliped of the resident individual and is probably a self-defense-related behavior. We conclude that cheliped laterality in O. saratan populations should be considered as a bimodal trait, where left- and right-handedness is not under natural selection pressure.

Hemolymph supply to locomotor muscles of the ghost crab, Ocypode quadrata

Ghost crabs are the fastest and most aerobically fit of the land crabs. The exceptional locomotory capacity of these invertebrate athletes seemingly depends upon effective coupling between the cardiovascular system and skeletal muscles, but how these systems are integrated has not been well defined. In the current study, we investigated the relationship between aerobic muscle fibers within the skeletal muscles used to power running and the blood vessels supplying these muscles. We used histochemical staining techniques to identify aerobic versus glycolytic fibers and to characterize membrane invaginations within the aerobic fibers. We also determined how the diameters of these two fiber types scale as a function of body size, across two orders of magnitude. Vascular casts were made of the blood vessels perfusing these muscles and special attention was given to small, capillary-like vessels supplying the fibers. Finally, we injected fluorescent microspheres into the hearts of living crabs and tracked their deposition into different muscle regions to quantify relative hemolymph flow to metabolic fiber types. Collectively, these analyses demonstrate that ghost crab muscles are endowed with an extensive arterial hemolymph supply. Moreover, the hemolymph flow to aerobic fibers is significantly greater than to glycolytic fibers within the same muscles. Aerobic fibers are increasingly subdivided by membrane invaginations as crabs increase in size, keeping the diffusive distances relatively constant. These findings support a functional coupling between a well-developed circulatory system and metabolically active muscle fibers in these invertebrates.

Autotomy induced effects on the locomotor performance of the ghost crab, Ocypode quadrata

The voluntary amputation of an appendage, or autotomy, is an effective defensive mechanism that allows an animal to escape aggressive interactions. However, animals may suffer long-term costs that can reduce their overall fitness. Atlantic ghost crabs (Ocypode quadrata) are one of the fastest terrestrial invertebrates, and regularly lose one or more limbs in response to an antagonist encounter. When running laterally at fast speeds, they adopt a quadrupedal gait using their 1st and 2nd pair of legs while raising their 4th, and sometimes the 3rd, pair of legs off the ground. This suggests that some limbs may be more important for achieving maximal locomotor performance than others. The goal of this study was to determine whether the loss of certain limbs would affect running performance more than others, and what compensatory strategies were used. Crabs were assigned to four different paired limb removal treatments or the control group and run on an enclosed trackway in their natural habitat. Ghost crabs were found to adjust stride kinematics in response to limb loss. Loss of the 2nd or 3rd limb pairs caused a reduction in running speed by about 25%, suggesting that the remaining intact limbs were unable to compensate for the loss of either limb, either due to lack of propulsive forces produced by these limbs or issues stemming from re-coupling limb arrangements. Loss of any of the other limbs had no detectable effect on running speed. We conclude that compensatory ability varies depending on the limb that is lost.

Impact of the fire ant pesticide AMDRO on loggerhead turtle nest productivity and seafinding orientation

Invasive fire ants prey on a variety of organisms in the southeastern USA, including the pipped eggs and hatchlings within sea turtle nests. The granular fire ant bait AMDRO® (active ingredient hydramethylnon) is currently used at some rookeries to protect nests, but no studies have been conducted to determine if the pesticide negatively impacts the eggs or the hatchlings. We examined the pesticide’s effect on loggerhead (Caretta caretta) nests at Juno Beach, Florida, USA, specifically targeting how exposure affected hatching success, hatchling emergence success, and the ability of the turtles to orient visually from the nest to the sea. Pesticide granules were placed within a 30 cm diameter circle on the sand directly above the nest during the final 5-10 days of incubation, representative of its typical application at nesting beaches. Cornmeal granules in soybean oil and untreated natural nests served as controls. AMDRO had no significant effect on hatching success or emergence success, nor did it result in any deficiencies in hatchling orientation accuracy. However, the pesticide and cornmeal control attracted other predators (Atlantic ghost crabs and avian species), in addition to fire ants, to the nest site, thus revealing the nest’s location and potentially increasing its vulnerability. Consequently, we suggest that its usage may not be beneficial at sites where predators other than ants are especially abundant.

Growling from the gut: co-option of the gastric mill for acoustic communication in ghost crabs

Animal acoustic communication systems can be built upon co-opted structures that become specialized for sound production or morphological novelties. The ghost crab, Ocypode quadrata , evolved a novel stridulation apparatus on the claws that is used during agonistic interactions, but they also produce a rasping sound without their claw apparatus. We investigated the nature of these sounds and show that O. quadrata adopted a unique and redundant mode of sound production by co-opting the gastric mill (grinding teeth of the foregut). Acoustic characteristics of the sound are consistent with stridulation and are produced by both male and female crabs during aggressive interactions. Laser Doppler vibrometry localized the source of maximum vibration to the gastric region and fluoroscopy showed movement of the gastric mill that coincided with stridulation. The lateral teeth of the gastric mill possess a series of comb-like structures that rub against the median tooth to produce stridulation with dominant frequencies below 2 kHz. This previously undescribed gastric stridulation can be modulated and provide a means of assessment during aggressive interactions, similar to the use of the claw stridulation apparatus. This functional redundancy of stridulation in crabs offers unique insights into the mechanisms of evolution of acoustic communication systems.

Quantitative methods for the determination of abundance of mobile prey of ghost crabs, Ocypode Weber, 1795 (Decapoda: Brachyura: Ocypodidae), a top predator on sandy shores

ABSTRACT Ghost crabs, OcypodeWeber, 1795 (Decapoda: Brachyura: Ocypodidae) are the top-benthic predators on sandy beaches in the sub-tropical and tropical regions around the world. They are omnivores and opportunistic feeders with varied feeding modes, such that they can exert cascading trophic effects on intertidal communities. Although there is a wealth of literature on the diet of ghost crabs based on qualitative reports of direct observation of predation, tracks/signs of feeding activities, or presence/absence data of prey items in foregut content analyses, there is hardly any quantitative analyses of food resources in the field that are available to these top predators on the sandy shore. While the abundance of immobile food resources can be ascertained by sediment sample assays, specialized sampling methods have been used for the collection and enumeration of mobile prey items. There is a need also to understand the period of foraging activity of the study species in order to track the predator-prey interaction at the appropriate time of the day. We outline three techniques suitable for the collection of prey types with different distribution, activity period and mobility: 1) surface-dwelling prey, 2) prey that burrow, and 3) prey that are capable of flying, a novel method that has not been utilized and described before.

KARAKTERISTIK HABITAT TEMPAT BERTELUR PENYU SISIK (Eretmochelys imbricata ) DI TAMAN WISATA ALAM TANJUNG KELUANG KECAMATAN KUMAI KALIMANTAN TENGAH

This research aimed to discover the characteristics of hawksbill turtle egg-laying place (Eretmochelys imbricata) in the Tanjung Keluang Nature Park of Kumai District Central Kalimantan. The data which is collected to describe the characteristics of the habitat covers the length of the beach, its width, its slope, the distance of the nest with the vegetation, the air humidity, the air temperature, the nest temperature, the moisture content of sand substrate, the texture of sand substrate, the water salinity, and other factors that threaten the hawksbill turtle egg-laying place habitat. From the location of the study, it was found that the length of the beach that becomes the egg-laying place is 5000 meters and 1200 meters that do not become the egg-laying place, the beach width is about 3 – 12 meters at the highest tide and 9 – 20 meters at the lowest tide, the slope of the beach where the nest is found ranges from 10 to 15% and 8 – 11% where the nest cannot be found, the nest distance with the vegetation is about 0 – 2 meters, the air humidity is around 94,7% - 68,8%, the air temperature is about 28,830C - 330C, the nest temperature is about 28,620C, the sand substrate texture is medium with 0,21 – 0,50 µm, and the sea water salinity is 27,5%. At the location of the study there was found that every hawksbill turtle nest located in a shade of sea pandan trees (Pandanus tectorius). Hawksbill turtles are threatened by predators such as monitor lizards (Varanus salvator), ghost crabs (Ocypoda sp), fishing activities, waste bins, and natural factors such as coastal abrasion and the presence of weeds growing on the beach surface. Keyword: Habitat Characteristics, Hawksbill turtle, Tanjung Keluang Natural Park

From carrion to Christmas beetles: the broad dietary niche of the red fox in a hybrid coastal ecosystem in south-eastern Queensland

The diet of the European red fox (Vulpes vulpes) was investigated through analysis of 1185 scats collected between 2010 and 2014 from coastal south-east Queensland, Australia. By both frequency of occurrence and volume, its diet was dominated by terrestrial arthropods, marine arthropods, vegetation and birds, although the remains of the short-tailed shearwater (Ardenna tenuirostris) consumed as carrion dominated the latter. Terrestrial arthropods, primarily insects of the order Coleoptera, were eaten all year (61% frequency of occurrence, FO) but varied seasonally (35–67%FO), mostly due to the consumption of large numbers of Christmas beetles (Anoplognathus spp.) in the summer months. Marine arthropods consisted almost entirely of ghost crabs (Ocypode spp.) and seasonal variation in consumption was evident (33–72%FO) and likely correlated with ghost crab abundance. Fruit and berries were an important food item for foxes all year but also varied seasonally (30–65%FO). The opportunistic diet of this fox population is discussed in the context of dietary differences, but common opportunism, reported in other Australian and overseas studies.