Homing behaviour in the sleepy lizard (Tiliqua rugosa): the role of visual cues and the parietal eye

To investigate how visual cues are integrated into a navigational strategy for homing in the Australian sleepy lizard (Tiliqua rugosa), lizards were displaced beyond their home range, either with full access to visual cues or with no access to visual cues during the displacement. Homeward orientation was significantly worse when lizards were denied visual cues during the displacement than when they were not. However when lizards were displaced with their field of view restricted to the sky, their homeward orientation was equally as good as that of lizards displaced with no visual restriction. These experiments suggest that sleepy lizards use celestial cues to determine the compass bearing of the outward journey, and reverse this bearing to orient in the homeward direction (course reversal). In a subsequent experiment, lizards oriented randomly with respect to home when the parietal eye was entirely covered with a patch during the displacement and return, while control lizards fitted with a sham parietal eye patch were well oriented towards home. In both groups, the lateral eyes were unobstructed and had complete access to visual cues including celestial cues and landmarks. These results suggest that the parietal eye plays a highly significant role in sleepy lizard homing, perhaps mediating a sky polarization compass sense.     

Estimating paternity with spatial behaviour and DNA fingerprinting in the striped plateau lizard, Sceloporus virgatus (Phrynosomatidae)

The association between spatial proximity and paternity was studied in a population of the striped plateau lizard, Sceloporus virgatus. The relationship between estimated mating success and male phenotypic traits was examined for a sample of 55 males. DNA samples were obtained from 13 female-offspring families. The males with the closest spatial proximity to each female were tested as possible sires within each family. Fingerprinting with two multilocus hypervariable minisatellite probes revealed a strong correspondence between male-female spatial proximity and actual paternity. Paternity could be assigned for 72 of the 100 hatchlings. Most hatchlings with identifiable sires were attributed to a male with the highest category of spatial proximity to the mother. However, there was a low to moderate level of multiple paternity within clutches, and for some clutches probable sires could not be identified even though the most likely behavioural candidates were tested. Thus, nonterritorial males or other males lacking strong social and spatial relationships with females may achieve some degree of reproductive success. Analysis of mating success revealed that male success increased with body size, up to a point beyond which larger size conferred no advantage. Received: 7 January 1997 / Accepted after revision: 16 June 1997     

Strategies of homing behavior in the red squirrel,Tamiasciurus hudsonicus

Summary Seventeen red squirrels (Tamiasciurus hudsonicus) were displaced and released about 600 or 2000 m from their home site, and the routes they followed during several hours after release were recorded. The analysis of these routes shows that, in their first attempts to leave the release site area, the squirrels' orientation is non-random with respect to the home direction (Fig. 2a). However, after a few hundred meters in this initial direction, the animals tend to go back to the release site area, and then to perform a series of radial forays centered on the latter.The results suggest that, in the conditions of the experiment, the squirrels have some information on the direction, but not on the distance to the home site. Their behavior appears to be governed by two complementary (but occasionally conflicting) strategies, one being to use the directional information available, the other not to proceed further than a distance which corresponds to the distance normally covered in spontaneous exploratory trips. It is argued that this double strategy is appropriate for spontaneous homing trips consecutive to an exploratory foray.     

Larval behavior of predacious sister-species: orientation,molting site,and survival in Chrysopa

Field and laboratory studies compared two features of larval behavior in a pair of predacious sisterspecies of green lacewings: one (Chrysopa slossonae) a specialist on a single species of colonial aphids (the woolly alder aphid) that occur on branches and trunks of alder trees, the other (C. quadripunctata) a general aphid feeder whose primary prey is dispersed on foliage of diverse types of trees. First, a few hours after hatching, larvae of the two species develop significantly different phototactic responses; the differences correspond well with the spatial distributions of their prey. Most C. slossonae exhibited negative phototaxis, a response that helps move hatchlings inward on alder trees toward the woolly alder aphid colonies, whereas most C. quadripunctata hatchlings showed positive orientation to light, a response that tends to keep them in tree canopies with their prey. Second, in greenhouse experiments, a significantly greater proportion of C. slossonae larvae (second instars) molted within woolly alder aphid colonies and remained with the aphids than did C. quadripunctata larvae. These differences indicate that the specialist larvae have evolved a high degree of behavioral fidelity to their prey. However, larvae (second instars) of the two species that were released near ant-tended woolly alder aphid colonies in the field had similar recovery (= survival) rates. Consequently, natural selection may not act on behavioral traits that influence larval fidelity to prey during the late second and early third instars.     

Host preference,site fidelity,and homing behavior of the symbiotically luminous cardinalfish,Siphamia tubifer (Perciformes: Apogonidae)

The sea urchin cardinalfish, Siphamia tubifer (Perciformes: Apogonidae), is unusual among coral reef fishes for its use of bioluminescence, produced by symbiotic bacteria, while foraging at night. As a foundation for understanding the relationship between the symbiosis and the ecology of the fish, this study examined the diel behavior, host urchin preference, site fidelity, and homing of S. tubifer in June and July of 2012 and 2013 at reefs near Sesoko Island, Okinawa, Japan (26°38′N, 127°52′E). After foraging, S. tubifer aggregated in groups among the spines of the longspine sea urchin, Diadema setosum, and the banded sea urchin, Echinothrix calamaris. A preference for D. setosum was evident (P < 0.001), especially by larger individuals (>25 mm standard length, P < 0.01), and choice experiments demonstrated the ability of S. tubifer to recognize and orient to a host urchin and to conspecifics. Tagging studies revealed that S. tubifer exhibits daily fidelity to a host urchin; 43–50 and 26–37 % of tagged individuals were associated with the same urchin after 3 and 7 days. Tagged fish also returned to their site of origin after displacement; by day two, 23–43 and 27–33 % of tagged individuals returned from displacement distances of 1 and 2 km. These results suggest that S. tubifer uses various environmental cues for homing and site fidelity; similar behaviors and cues might be used by larvae for recruitment to settlement sites and for the acquisition of luminous symbiotic bacteria.     

Variation in homeward orientation performance in the sleepy lizard (Tiliqua rugosa): effects of sex and reproductive period

Sleepy lizards are monogamous skinks which show high pair fidelity. This study reveals inter- and intrasexual differences in homeward orientation performance in this lizard. Male and female lizards were displaced during three phases of the spring activity period, the pre-pairing, pairing/mating, and post-pairing periods. All groups (with the exception of post-pairing males) were significantly oriented homewards, but males were significantly better oriented towards home than females during the pairing period. Furthermore, males were significantly better homeward oriented during the pre-pairing and pairing periods than in the post-pairing period. Similar results were observed for rate of movement away from the release site. In sleepy lizards, sex-based differences in homing behaviour are unlikely to be attributable to differences in the area of familiarity, or availability of orientation mechanisms. However differences in homing motivation may explain these differences. Males may miss mating if absent from the home range during the pre-pairing and pairing periods, while females may still be able to obtain a mating even when absent. Females however may be more motivated than males to return to the familiar home range during the post-pairing period to ensure efficient feeding during internal embryo development. Received: 16 February 1998 / Accepted after revision: 28 March 1998     

Heterospecific call recognition and phonotaxis in the orientation behavior of the marbled newt,Triturus marmoratus

The role of acoustic cues as reference cues for orientation by amphibians has been demonstrated in anurans, the only amphibian group that engages in acoustic communication, but not in urodeles. Orientation responses of marbled newts, Triturus marmoratus, were studied to determine whether heterospecific calls elicited positive phonotaxis. The orientation tests consisted in presenting either a familiar acoustic stimulus, the advertisement calls of natterjack toads (Bufo calamita), or a control stimulus, the advertisement calls of European green toads (Bufo viridis) that the newts would not be expected to recognize. Marbled newts and natterjack toads occur in simpatry, but T. marmoratus and B. viridis are allopatric species. Thus, T. marmoratus is distributed over the northern half of the Iberian Peninsula, whereas B. viridis occurs in the Balearic Islands, but not over the Iberian Peninsula. Newts were released in a circular arena while a recorded chorus of natterjack toads or European green toads played outside the arena to determine whether they displayed positive phonotactic orientation. Our results show that marbled newts performed positive phonotaxis when exposed to the breeding calls of natterjack toads, but not to those of European green toads. Newts chose a compass course in the direction of the advertisement calls of B. calamita. Acoustic information might improve orientation accuracy. This study is the first to provide evidence of heterospecific call recognition and positive phonotactic response in urodeles.Communicated by W. Wiltschko     

The role of trail following in the homing of intertidal chitons: A comparison between threeAcanthopleura spp.

Three species of intertidal tropical chitons observed between 1984 and 1986, exhibit different movement patterns:Acanthopleura gemmata (Indian and Pacific Ocean) is a strict homer;A. granulata (Caribbean Sea) is mostly a ranger but sometimes shows homing behaviour;A. brevispinosa (Western Indian Ocean) alternates homing and ranging for different excursions. The three species have been studied in the field using a motographic technique to assess the importance of intra-individual trail following in homing. The fraction of the path which overlaps with earlier segments of an individual's trail is different in the three species: when returning from feeding groundsA. gemmata follows almost the whole of the outgoing path; inA. granulata the path coincidence is minimal, whileA. brevispinosa shows intermediate trail following values. InA. gemmata andA. brevispinosa trail overlap rises rapidly just after feeding, and trail following is mostly backward along the outgoing path. On the other hand,A. granulata shows a linear increase in trail coincidence with increasing path covered and the proportion of forward trail following is relatively higher. Nevertheless, all specimens of the three species which show a high homing performance invariably show a large trail following also. These findings confirm that, despite the interspecific difference in ecology and the related variation in spatial organization of foraging excursions, trail following is the basic mechanism for homing in intertidal chitons.     

The role of size and aggression in intrasexual male competition in a social lizard species, Egernia whitii

Competition between males is a key component of the agonistic intrasexual interactions that influence resource acquisition, social system dynamics, and ultimately reproductive success. Sexual selection theory predicts that traits that enhance success in intrasexual competition (particularly male–male competition) should be favored. In vertebrates, this often includes body size and aggression, with larger and/or more aggressive males outcompeting smaller or less aggressive conspecifics. The majority of studies consider aggression as a flexible trait which responds to local social or environmental conditions. However, aggression frequently shows considerable within-individual consistency (i.e., individuals have identifiable aggressive behavioral types). Little is known about how such consistency in aggression may influence competition outcomes. We integrated a detailed field study with a laboratory experiment to examine how a male’s aggressive phenotype and his size influence competitive interactions in Egernia whitii, a social lizard species which exhibits strong competition over resources (limited permanent shelter sites and basking sites). Individual aggression and size did not predict competition outcome in the laboratory nor did they predict home range size, overlap, or reproductive success in the field. However, winners of laboratory trial contests maintained consistent aggressive phenotypes while consistency in aggression was lost in losers. We suggest that aggression may be important in other functional contexts, such as parental care, and that alternative traits, such as fighting experience, may be important in determining competition outcome in this species.     

Ectoparasite loads in free-ranging northern fence lizards, Sceloporus undulatus hyacinthinus: effects of testosterone and sex

More knowledge of the proximate factors that influence parasite loads would help us understand the selective pressures faced by hosts and host-parasite evolution. Testosterone has been associated with increased parasite loads in vertebrates. Here we asked whether experimentally elevated testosterone affected ectoparasite loads in free-ranging northern fence lizards (Sceloporus undulatus hyacinthinus). Males were captured, given testosterone or sham implants, and released. In 2 consecutive years, testosterone-implanted males had significantly more ectoparasites at recapture than did controls. Additionally, ectoparasite loads were positively correlated with testosterone concentrations in unmanipulated males, and males had significantly more ectoparasites than did females. The results are consistent with an effect of testosterone on parasite loads. However, rather than elevated testosterone increasing mite loads in experimental males, it appeared that high testosterone inhibited a natural seasonal decline in mite loads. Testosterone-implanted males also lost body mass whereas controls gained mass. Among controls, those retaining the most ectoparasites over the course of the experiment experienced the smallest gains in body mass, suggesting that the mites are costly.     

Relatedness and avoidance of inbreeding in the lizard, Tiliqua rugosa

Two potential mechanisms for reducing the level of inbreeding, sex-biased dispersal and kin avoidance, were examined in the Australian sleepy lizard, Tiliqua rugosa. The home range centres, and the genotypes at four polymorphic microsatellite DNA loci were determined for adult lizards in a 70-ha study area near Mount Mary, South Australia. From estimates of genetic relatedness, females were as closely related to other females as they were to males, both within the whole study area, and within home ranges. Similarly, males were as closely related to other males as they were to females. This suggests that dispersal in the population is not sex-biased. Sleepy lizards form monogamous pairs during the spring. Partners were less closely related to each other than to other potential partners in the home range area. This suggests active choice of unrelated partners. The mechanism for recognising related from unrelated individuals is unknown, but the behaviour could reduce inbreeding. Received: 7 November 1998 / Accepted: 30 May 1999     

Foraging and homing behaviour in the high-shore, crevice-dwelling limpet Helcion pectunculus (Prosobranchia: Patellidae)

The foraging activity of the high-shore, crevice-dwelling limpet Helcion pectunculus (Gmelin, 1791) (Prosobranchia: Patellidae) from an exposed shore on the eastern Cape coast of South Africa was monitored. Activity was compared during spring and neap tides and between spring, summer, autumn and winter. Rhythms of activity in this limpet varied depending upon microhabitat; individuals inhabiting both east- and west-facing rock surfaces were active during nocturnal low tides, but limpets on west-facing rock surfaces were also active during daytime low tides, whilst in the shade. Individuals travelled further during foraging excursions in winter (xˉ=85.53 cm) than in either spring (xˉ=55.7 cm) or summer (xˉ=48.8 cm) and also during spring low tides (xˉ=89.8 cm) compared with neaps (xˉ=40.9 cm). H. pectunculus exhibited rigid homing to a fixed scar within a crevice, and feeding excursions were found to consist of three distinct phases: a relatively rapid outward phase, a much slower foraging phase and a rapid homeward phase. Whether or not these limpets graze throughout an excursion is not known. Foraging was always highly directional, with a mean vector which took limpets onto an area of the rock face with the highest microalgal biomass. The fact that H. pectunculus took advantage of optimal feeding areas and memorized their location to enable return visits suggests a learning component in herbivorous gastropod foraging behaviour. Received: 29 December 1997 / Accepted: 8 May 1998     

The role of synchronized calling,ambient light,and ambient noise,in anti-bat-predator behavior of a treefrog

Summary Male treefrogs, Smilisca sila (Hylidae), produce calls of varying complexity and demonstrate a remarkable ability to synchronize their calls with those of neighbors. The bat Trachops cirrhosus eats frogs and uses the frogs' advertisement calls as locational cues. The bats are less likely to respond to synchronous calls than to asynchronous calls, and when given a choice prefer complex calls to simple calls.Experiments with bat models indicate that, like other frogs, S. sila probably uses visual cues to detect hunting bats. In response to bat models the frogs decreased both the number and the complexity of their calls. The calling behavior of the frogs was sampled in the field during periods with and without artificial illumination. The frogs produced fewer and less complex calls, and they tended to call from more concealed sites, during the period without illumination, when presumably it would have been more difficult for the frogs to detect hunting bats. S. sila tended to call from sites with higher ambient noise level, the noise primarily originating from waterfalls. The frequencies of the dominant energies in the waterfall sounds completely overlapped the frequency range of the S. sila call; thus waterfalls might mask the frog calls. When given a choice between calls produced near and away from waterfall sounds, bats preferred the latter.     

Bimodal orientation and the occurrence of temporary reverse bird migration during autumn in south Scandinavia

Extensive ringing data from a coastal site (Falsterbo Bird Observatory) in southwesternmost Sweden were used to investigate the occurrence of reverse autumn migration among 20 passerine bird species of widely different migration categories. The data demonstrate that reverse migration is a widespread and regular phenomenon among nocturnal as well as diurnal migrants and among irruptive migrants, temperate zone migrants, and long-distance migrants destined for tropical winter quarters. The reoriented movements were directed approximately opposite to the normal migration direction, i.e. between NNW and ENE from the coast and towards inland. Median distances of reverse movements varied between 9 and 65 km. Some individuals of irruptive and partial migrants settled to winter in the reverse direction. Bird species with relatively small fat reserves at capture were more likely to perform reverse migratory movements than species with larger fat deposits. In two species birds performing forward migration were significantly heavier within 10 days after capture than individuals performing reverse movements. The reoriented movements probably are of adaptive significance for birds confronted with the sea and pre-disposed to refuelling during migration. A bimodal orientation mechanism will bring the birds from an area with high competition for food and high predation risk to more suitable resting and feeding grounds before resuming migration in the forward direction and crossing the barrier. Received: 11 July 1995/Accepted after revision: 19 November 1995     

Home range overlap of mothers and their offspring in the sleepy lizard, Tiliqua rugosa

This paper reports a field investigation of interactions between juveniles and their mothers in the Australian sleepy lizard, Tiliqua rugosa. In their first spring season, juvenile lizards maintain home ranges largely within the home range of their mother. Juvenile home ranges are significantly smaller than those of adult males and females, and juveniles move significantly less often and significantly shorter distances than adults. While siblings were never found together in the spring, they showed a significant tendency to be closer to each other than if they were randomly located in their home ranges. Juveniles and mothers were never found together, nor was there any evidence for any positive (or negative) spatial association. Nevertheless, the extended tolerance of home range overlap represents a greater degree of mother-offspring association than has been previously reported for other lizards. Despite this, the level of parental care can only be described as minimal. Received: 20 June 1997 / Accepted after revision: 29 December 1997     

Multiple spawning events and sexual reproduction in the octocoral Sarcophyton elegans (Cnidaria: Alcyonacea) on Lizard Island, Great Barrier Reef

Sarcophyton elegans is a common symbiotic (zooxanthellate) octocoral species in the shallow waters of the Great Barrier Reef (GBR). Study of a population at Lizard Island (14°40′S, 145°28′E) on the GBR from October 1991 to January 1994 revealed that, as is typical of tropical alcyonarian corals, S. elegans is a gonochoric broadcast spawner with a 1:1 sex ratio. Sexual reproduction was closely correlated with colony size, with first reproduction at 13-cm basal stalk circumference for females and 12 cm for males. Oogenesis took 19–24 months, with a new cycle commencing every year, and spermatogenesis took 10–12 months. The majority of gametes were released during the annual austral mass coral spawning event after the full moon in November, but gametes were also released after the full moon in each month between August and February. All autozooid polyps participated in reproduction, but those at the outer edge of a colony released their gametes first. During subsequent months, the polyps closer to the center of the colony released their gametes. This is a novel strategy of gamete release, reported here for the first time, which accommodates the demands of feeding and reproduction in a different way than other corals where individual polyps have separate feeding or reproductive roles. Colonies upstream in the prevailing current spawned up to 1 month earlier than those downstream and ceased 1 month earlier. The mechanism controlling this spatial differentiation in spawning time, repeatedly observed over three seasons, is unknown. Sarcophyton elegans appears to have a dual strategy of providing protection for its gametes by releasing most of them concurrently with the single, annual mass spawning of a large number of cnidarians, while also hedging its bets by individual colonies spawning a fraction of their gametes over an extended period of 6 months.     

Interspecific hybridization in ants: at the intersection of ecology, evolution, and behavior

Ants are social and are haplodiploid. This combination may allow the evolution of a variety of unusual genetic pathways to achieve reproductive success. These include hybridizing across species, differential use of sperm to create a hybrid worker population, and reproductively isolated gene pools that depend on each other for their survival. Although there are demonstrable costs for colony development and reproduction, these phenomena may nevertheless be relatively common in nature. The specific ecological advantages that favor the evolution of these reproductive modes remain to be discovered.