Effects of inter-pond distance on the breeding ecology of tungara frogs

Habitat and resource distributions can influence the movement and aggregation of individuals and thus have important effects on breeding behavior and ecology. Though amphibians have been model systems for the study of breeding behavior and sexual selection, most studies have examined breeding behavior within a single pond. As a result, little is known about how inter-pond distance affects breeding amphibians. We studied the effects of inter-pond distance on the breeding ecology of the tungara frog, Physalaemus pustulosus, in replicated pond arrays in which distance was varied from 0 to 50 m. We predicted that male site fidelity and male aggregation within arrays would increase with inter-pond distance, and that the opportunity for mate choice and oviposition site selectivity by females would decrease with the distance between ponds. Male site fidelity did increase with inter-pond distance. However, male aggregation decreased with distance, such that males tended to be more evenly spaced among ponds when ponds were farther apart. The opportunity for mate choice by females, measured as the number of males within the phonotactic radius of females, also decreased with inter-pond distance. Each of these three responses was consistent with a threshold effect between 5 m and 10 m in inter-pond distance. This threshold corresponded to the maximum distance at which females in laboratory choice experiments exhibited phonotaxis toward the ”whine” call of a tungara male, suggesting that phonotactic limits may play an important role in tungara movements and spacing patterns. The distribution of egg masses among ponds, a potential correlate of oviposition site selectivity, did not vary with inter-pond distance. Multiple egg masses deposited on the same night were significantly overdispersed in all distance treatments, implying that females may select oviposition sites to avoid conspecific egg masses over distances of at least 50 m. Collectively, these results demonstrate that inter-pond distance may indeed affect amphibian breeding and movement behavior, and that consideration of multiple habitat patches and their spatial distributions can provide new insights into even the most well-understood mating systems. Received: 9 January 1999 / Accepted: 1 August 1999     

Wind distribution of the egg masses of Chironomus anthracinus (Zetterstedt) (Diptera: Chironomidae) in a shallow, wind-exposed lake (Loch Leven, Kinross)

A mass emergence of Chironomus anthracinus (Zetterstedt) took place at Loch Leven, Kinross, in late May and early June 1971, leading to a large concentration of egg masses. The distribution of egg masses within the lake was determined on 6 June 1971 and the accumulation of egg masses along wind-exposed shores, under the influence of a 17–23 km h^?1 wind, was noted. Oviposition site selection by the weak flying adults appears to have little importance upon the final distribution of larvae within the lake. Temporary planktonic activity of first instar larvae under the influence of wind-induced water currents is briefly discussed as a dispersal mechanism in the light of observed egg mass accumulation in the lake.     

Inference of adult female dispersal from the distribution of gypsy moth egg masses in a Japanese city

1 The native range of the gypsy moth Lymantria dispar (L.) spans the temperate forests of Eurasia. Across this region, a clinal female flight polymorphism exists; gypsy moth females in eastern Asia are mostly capable of directed flight, those in western and southern Europe are largely incapable of flight and populations distributed across the centre of the distribution exhibit a range of intermediate flight behaviours. 2 Although information exists about the timing and duration of female flight from laboratory and wind tunnel studies, little or no quantitative data are available on average distances flown by Asian gypsy moth females prior to oviposition in the field. This information is critical for estimating risk of contamination at specific ports and transit terminals, as well as for predicting the spread of populations that might someday invade currently uninfested regions of the world. 3 In the present study, an extensive visual survey of gypsy moth egg masses was conducted during a walk through streets and paths in a 3.92 × 5.76 km area in Kanazawa, Japan. This area consisted of a matrix of urban, agricultural and forest land uses. The distribution of egg masses relative to distances from host forests was used to infer the magnitude of pre‐ovipositional female flight. 4 A total of 3172 egg masses was recorded from surveys conducted during the search of a path totalling 384 km. Within urban areas, egg masses were most abundant in the area <1 km from the edge of forest land. 5 These results suggest that most female gypsy moth flight is limited to the area within 1 km of host forests. They also suggest that shipping containers and other parcels located >1 km from forests are at a much lower risk of contamination with Asian gypsy moth egg masses.     

Reproductive activity of Strombus gigas (Mesogasteropoda: Strombidae) in differente habitats of Alacranes reef, Yucatán

The spawning relationships with temperature/photoperiod of Strombus gigas were investigated considering three habitats in Alacranes Reef, Yucatan, between February 1999 and March 2000. The sites were 22 degrees 34'N, 89 degrees 42'W (site 1); 22 degrees 29'N, 89"45'W (site 2) and 22 degrees 22'N, 89 degrees 39'W (site 3). At each site, transects (100 m x 10 m) were done. Different kinds of reproductive behavior of S. gigas was observed: such as copulating and egg-laying. Individuals alone and egg masses were registered as well. The S. gigas shell length and lip thickness were measured. High density of adults was found at site 2 with 87 conchs in one transect of 1000 m2. The mean density per m2 was 0.004 for site 1; 0.035 for site 2; and 0.003 for site 3. The mean shell length was 220 mm and the lip thickness mean was 16 mm (N = 783) for all sites. In February 1999 egg-laying female was found on sand. There was a high reproductive activity at site 2 with 8 egg-laying and 18 egg masses. Minimum reproductive activity was found at site 3 with 2 egg masses. The bottom-water temperature was related positively with copulating pairs (r = 0.723, f = 11.05, p < 0.01) and egg masses (r = 0.736, f = 11.82, p < 0.1). Correlation between photoperiod with copulating pairs (r = 0.857, f = 27.78, p < 0.01) and egg masses (r = 0.782, f = 15.77, p < 0.01) were found as well.     

Effects of current velocity on development and survival of lingcod,Ophiodon elongatus,embryos

Synopsis The influence of current velocity on the survival and development of lingcod embryos was investigated in the field and laboratory. Examination of egg masses at five lingcod spawning sites indicated that embryo mortalities were high (up to 95%) at low-current sites because of inadequate ventilation and resulting hypoxia. Development of embryos near the center of poorly ventilated egg masses was retarded relative to development of embryos near the periphery. Hatching of embryos from poorly ventilated eggs was protracted; embryos from the interior of egg masses hatched later and were significantly smaller than embryos from eggs near the periphery. Oxygen levels measured in egg masses at low-current velocity sites during tidal flow average 16% air saturation, corresponding to a Median Tolerance Limit (LT₅₀) of about 73 h. Oxygen levels measured in egg masses at high-current velocity sites during slack water average 69% air saturation, a level that did not adversely affect the embryos. Current velocities of 10–15 cm s^–1 were needed to maintain interstitial oxygen levels in egg masses near that of the ambient water. Water movement may be an important stimulus for spawning site selection by lingcod. In areas where tidal currents were weak, spawn deposition occurred in shallow water where waves and vertical tide motion created water movement. In areas where tidal currents were strong, spawns were consistently deposited in deeper water.     

Biochemical and molecular characterization of serine proteases from larvae of Chrysomya bezziana, the Old World Screwworm fly

The diversity of serine proteases secreted from Chrysomya bezziana larvae was investigated biochemically and by PCR and sequence analysis. Cation-exchange chromatography of purified larval serine proteases resolved four trypsin-like activities and three chymotrypsin-like activities as discerned by kinetic studies with benzoyl-Arg-p-nitroanilide and succinyl-Ala-Ala-Pro-Phe-p-nitroanilide. Amino-terminal sequencing of the three most abundant fractions gave two sequences, which were homologous to other Dipteran trypsins and chymotrypsins. Analysis of products generated by PCR of cDNA from whole larvae using specific primers based on the amino-terminal sequences and generic serine protease primers identified 22 different sequences, while phylogenetic analysis of the deduced amino acid sequences differentiated two trypsin-like and four chymotrypsin-like families. Phylogenetic comparisons with Dipteran and mammalian serine protease sequences showed that all the Chrysomya bezziana sequences clustered with Dipteran sequences. The Chrysomya bezziana chymotrypsin-like sequences segregated within a Dipteran cluster of chymotrypsin sequences, but were well dispersed amongst these sequences. The largest Chrysomya bezziana serine protease family, the trypB family, clustered tightly as a group, and was closely related to a Lucilia cuprina trypsin but distinct from Drosophila melanogaster alpha and beta trypsins. The trypB family contains ten highly homologous sequences and probably represents an example of concerted evolution of a trypsin gene in Chrysomya bezziana.     

Cytogenetic variation in natural populations of the Old World screwworm fly Chrysomya bezziana (Diptera: Calliphoridae).

The existence of sibling species in the Old World screwworm fly Chrysomya bezziana would raise serious problems in eradicating this pest if it entered Australia. Cytogenetic variation in C. bezziana was investigated by analyzing pupal trichogen polytene chromosomes. Natural populations of C. bezziana spanning its range from southern Africa to Papua New Guinea were examined as well as hybrids between a New Guinea laboratory strain and natural populations. No evidence of sibling species was found. All populations exhibited the same basic banding pattern as the standard sequence established from a Papua New Guinea strain. Extensive asynapsis of chromosome homologues was found in some hybrid crosses and was therefore measured in all populations and hybrids to detect systematic variation. Asynapsis levels in most hybrids could not be statistically distinguished from those present in the parent populations except for crosses between populations at the ends of the range. This result does not permit asynapsis levels to be used in establishing the origin of introduced flies by estimating their distance from known populations. One inversion polymorphism and six band polymorphisms spread over three chromosomes were analyzed. Populations in each sampled region had characteristic combinations of band polymorphisms. This may offer a diagnostic method for determining the origin of flies accidentally introduced to Australia.     

玉米螟赤眼蜂的寄生卵块在玉米上的田间分布型

玉米螟赤眼蜂是松辽平原玉米带寄生亚洲玉米螟卵的优势种。通过几年来的田间释放结果,取得优异的成效。通过对它在玉米田间的分布型研究,揭示了它在玉米田间第一代螟卵发生期间的分布规律,为以疏松的寄生卵块集团形式呈聚集分布;集团内寄生卵块的分布是随机的,无论在高密度时,还是在一般密度条件下,均为聚集分布型;它不受风向的影响。这一研究结果为它的田间释放和应用技术提供重要的科学依据。     

Oviposition in three species of limnephiloid caddisflies (Trichoptera): hierarchical influences on site selection

1. Oviposition site selection was studied in three trichopteran species; an undescribed species of Hydatophylax (Limnephilidae), Onocosmoecus unicolor (Limnephilidae) and Neophylax rickeri (Uenoidae), in two Coastal Range streams in California, U.S.A. 2. Hydatophylax sp. egg masses were generally found at or above the water surface on substrata near the bank in pools, where undercut banks, overhanging vegetation and rocks shaded attachment sites and provided wind protection. Onocosmoecus unicolor females deposited their egg masses exclusively above the water on moist emergent wood. The egg masses of N. rickeri were almost exclusively found in high velocity areas of riffles, where females oviposited under water and attached their egg masses to the submersed undersides of unembedded, protruding stones with large emergent surfaces. 3. For Hydatophylax sp. and N. rickeri, a hierarchical selection scheme is proposed in which females use cues at three different spatial levels (stream, stream subunit, substratum) to choose oviposition sites. Females of O. unicolor seemed to choose at only two different levels of spatial resolution (stream, substratum). 4. The formation of large aggregations of egg masses in N. rickeri and O. unicolor suggests that females actively choose oviposition sites where conspecific egg masses are already attached. The clustering of egg masses may minimise the risk of predation through the dilution effect, because egg masses of N. rickeri and O. unicolor are both attacked by dipteran predators. 5. Females of the three Trichoptera species studied are able to make a clear choice of oviposition site in the heterogeneous stream environment. In comparison with other stream microhabitats, these are characterised by stable and relatively predictable environmental conditions during the time of egg development, which is seen as the main selective pressure leading to the observed egg‐laying behaviour.     

Insights into the mating habits of the tiger salamander (Ambystoma tigrinum tigrinum) as revealed by genetic parentage analyses

Among urodeles, ambystomatid salamanders are particularly amenable to genetic parentage analyses because they are explosive aggregate breeders that typically have large progeny arrays. Such analyses can lead to direct inferences about otherwise cryptic aspects of salamander natural history, including the rate of multiple mating, individual reproductive success, and the spatial distribution of clutches. In 2002, we collected eastern tiger salamander (Ambystoma tigrinum tigrinum) egg masses (> 1000 embryos) from a approximately 80 m linear transect in Indiana, USA. Embryos were genotyped at four variable microsatellite loci and the resulting progeny array data were used to reconstruct multilocus genotypes of the parental dams and sires for each egg mass. UPGMA analysis of genetic distances among embryos resolved four instances of egg mass admixture, where two or more females had oviposited at exactly the same site resulting in the mixing of independent cohorts. In total, 41 discrete egg masses were available for parentage analyses. Twenty-three egg masses (56%) consisted exclusively of full-siblings (i.e. were singly sired) and 18 (44%) were multiply sired (mean 2.6 males/clutch). Parentage could be genetically assigned to one of 17 distinct parent pairs involving at least 15 females and 14 different males. Reproductive skew was evident among males who sired multiply sired clutches. Additional evidence of the effects of sexual selection on male reproductive success was apparent via significant positive correlations between male mating and reproductive success. Females frequently partitioned their clutches into multiple discrete egg masses that were separated from one another by as many as 43 m. Collectively, these data provide the first direct evidence for polygynandry in a wild population of tiger salamanders.     

Variations in fecundity over catchment scales: Implications for caddisfly populations spanning a thermal gradient

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Host age and host selection byTrichogramma nubilale

Selection byTrichogramma nubilale (Ertle & Davis) for different aged egg masses ofOstrinia nubilalis (Hübner) was examined by separating components of parasitism. FemaleT. nubilale were exposed to egg masses of 2 different ages (freshly laid egg masses versus 1, 2, 3 or 4 day old egg masses), and the age of the initial egg mass inspected, number and percent of eggs and egg masses parasitized, and the emergence rate of pharate parasitoids was recorded. When there was a large difference in age between young and old egg masses, ♀♀ inspected initially more young egg masses (>2 days difference), parasitized a greater percent of young egg masses (>2 days difference), and parasitized more eggs/parasitized egg mass in young egg masses (>3 days difference) than old egg masses. Females did not discriminate between host age when hosts were similar in age. Successful emergence of parasitoids was greater from younger eggs than older eggs, although emergence was better from one-day-old eggs than from fresh eggs. These results imply that when the hosts were sufficiently different in age, ♀♀ were attracted to younger egg masses more than older egg masses, and they tended to remain ovipositing for longer periods of time on younger egg masses than older egg masses. Moreover, ♀♀ appeared to prefer to oviposit in hosts in which their young are more likely to complete development.      

Mating behaviour and mating success in woodfrogs Rana sylvatica

Mating behaviour of woodfrogs was investigated in a woodland pond in southeastern Michigan. Males became sexually mature one year before females and outnumbered females by 5.6 to 1 at the breeding site. Males employed searching behaviour to obtain mates. Yearly male mating success varied from 0 to 2 matings, and larger males had a greater probability of mating than smaller males. The mating season lasted less than 10 days. Most egg masses were deposited in 1 m² of a 256-m² pond. Experimental introduction of egg masses to the breeding site indicated that presence of eggs was sufficient to stimulate egg deposition. The influence of selection for synchronous sexual receptivity in females, communal egg deposition, and delayed female sexual maturation on male mating behaviour and variation in male mating success is discussed.     

Oviposition site selection by herbivorous beetles: a comparison of two thistle feeders, Cassida rubiginosa and Henosepilachna niponica

In insects that feed on plants in both adult and larval stages, it is often difficult to distinguish oviposition preference from adult feeding preference, because oviposition can occur at or in proximity to feeding sites. In the present study, characteristics of oviposition site selection of two beetle species, Cassida rubiginosa Müller (Coleoptera: Chrysomelidae) and Henosepilachna niponica (Lewis) (Coleoptera: Coccinellidae), were investigated in the field and laboratory, with particular attention to relationships with adult feeding sites. In the field, distances between adult feeding scars and egg masses differed for C . rubiginosa and H . niponica , with the former being very small and the latter averaging 24.6 cm. The same tendencies for the distances between adult feeding scars and egg masses of the two beetle species were confirmed in cages in which only female beetles were released. Cassida rubiginosa restricted egg laying to host plants in the field and to leaves in laboratory assays. On the other hand, H . niponica placed 8% of egg masses on plants adjacent to host plants in the field and often placed eggs on artificial substrates rather than leaf discs in laboratory assays. These results suggest that oviposition and female feeding sites are virtually inseparable in the case of C . rubiginosa , while H . niponica females do not necessarily keep to host plant leaves as oviposition substrates and they tend to oviposit at some distance from their feeding sites. Results are discussed in relation to proximate and ultimate causes of host selection behavior.     

Sex allocation in Telenomus busseolae, a solitary parasitoid of concealed eggs: the influence of host patch size

Telenomus busseolae Gahan (Hymenoptera: Scelionidae) is an important egg parasitoid of noctuid stem borers of gramineous crops, attacking egg masses of Sesamia spp. Under natural conditions, and whatever the host species attacked, these egg masses are generally concealed under the leaf sheaths or other narrow spaces, and vary greatly in size. In the work presented here, the influence of host patch size (4, 8, 16, 32, 64, or 128 eggs per mass) on the sex ratio and sex sequence pattern of ovipositing T. busseolae was investigated in the laboratory using Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae) as host. The results are similar to those described for other parasitoids of aggregated hosts, and are in accordance with the Local Mate Competition model. With increasing egg mass size, the overall sex ratio (proportion of males) decreased, although additional males were laid at the end of the sequence in the larger masses (64 and 128 eggs). Sex sequence pattern always followed a males‐first strategy, i.e., with a higher proportion of males at the beginning, but the whole sex ratio sequence was influenced by the size of the egg mass. Such results in a parasitoid of concealed eggs are compared to those observed in parasitoids of exposed eggs and discussed in terms of parasitoid reproductive strategies and evolutionary adaptations.     

Form, function, and embryonic migration in large gelatinous egg masses of arenicolid worms

Abstract. Attachment and gas exchange are design problems for the spheroidal egg masses that annelids and molluscs tether in sediments. At an intertidal site in Bodega Harbor, a high proportion of masses of arenicolid worms became detached, but they were not stranded higher than attached masses, and the embryos developed to advanced stages. The large masses, weighing 100–200 g, challenge predictions on limiting size for oxygen supply by diffusion. The estimated concentrations of embryos and thickness of the embryo layer exceed the limits predicted by a simple model for oxygen supply by diffusion from the surrounding water, but several features may enhance oxygen supply to embryos. (1) There is an internal cavity. Distal tears in the gel layer admit pulses of water into the center, thus adding an inner surface for gas exchange. (2) The motile embryos aggregate near the outer and sometimes inner surfaces of the gel layer. Embryos migrate in the gel toward regions of greater oxygen concentration. (3) Pennate diatoms colonize the masses, coating the surfaces and penetrating into the gelatinous matrix. Photosynthesis can exceed respiration when a mass is in the light. The pH in gel changes diurnally from a low of ∼7 to as much as 9.5, indicating an excess of respiration over photosynthesis at night and at least sometimes an excess of photosynthesis over respiration by day.     

The drift of some chironomid egg masses (Diptera: Chironomidae)

SUMMARY. The drift of chironomid egg masses was investigated in the River Mole (Devon) and the River Wye (Powys) in 1981. Large numbers of egg masses were found in the drift just after dusk; on one occasion an estimated 50,000 egg masses passed a sampling point in 5 h. Oviposition of free-floating egg masses appeared to be initiated and synchronized by the onset of darkness. Egg masses of some Pentaneurini (Tanypodinae), Tanytarsini and Chironomini (Chironominae) were found in the drift and adhering to submerged stones.
Flotation by means of a gas vacuole within the egg mass was observed in the Polypedilum 'convictum' group. The gas vacuole decreased in size over 8–11 h and the egg masses sank after 2–3h.
Some chironomid egg masses are capable of drifting large distances after oviposition. The implications of sueh drift are briefly discussed in relation to the distribution of chironomid larvae.     

Short- and long-range dispersal of medfly, Ceratitis capitata (Dipt., Tephritidae), and its invasive potential

Abstract:  Data were obtained from mark recapture trials pertaining to the dispersal of medfly, Ceratitis capitata (Dipt., Tephritidae), over both short (10–160 m) and very long distances (0.5–9.5 km) within the surveillance trapping array in Adelaide, Australia. They could be related to previously reported data sets by expressing the capture rates of each set in common terms that corrected for differences in recapture rate resulting from type of trap, season or climate. The mean capture rate at each distance from the point of release in each data set was expressed as a percentage of the real or inferred rate of that set at a distance of 100 m. The resulting distribution of dispersal distances conformed to both an inverse power model and a modified Cauchy model regardless of whether the present and previous data were combined or not. The modified Cauchy model inferred that the median distance flown was extremely short and 90% of flies displaced only 400–700 m despite the fact that a consistent trend in declining catch rates was obtained up to 9.5 km. The spread of invading propagules in quarantined zones in the first generation is likely to be limited by a decline to non-viable density within 1 km or less of the incursion point and the spread of larger infestations could be limited by the longevity of the dispersers. The results also have significance to the ability of surveillance trapping arrays to detect infestations and also to methods of distributing insects for the 'sterile insect technique'.