Seasonal shifts in clutch size and egg size in the side-blotched lizard,Uta stansburiana Baird and Girard

Summary There is evidence that the side-blotched lizard, Uta stansburiana, and some other organisms of temperate latitudes produce fewer and larger eggs as the reproductive season progresses. There are at least two models that could explain this phenomenon.Proponents of the parental investment model claim that females are selected to increase egg size, at the cost of clutch size, late in the season in order to produce larger and competitively superior hatchlings at a time when food for hatchlings is in low supply and when juvenile density is high. In this model the selective agent is relative scarcity of food available to hatchlings late in the reproductive season, and the adaptive response is production of larger offspring.The alternative explanation (bet-hedging model) proposed in this paper is based on the view that the amount of food available to females for the production of late-season clutches is unpredictable, and that selection has favored conservatively small clutches in the late season to insure that each egg is at least minimally provisioned. Smaller clutches, which occur most frequently late in the season, are more likely to consist of larger eggs, compared to larger clutches, for two reasons. Firstly, unlike birds, oviparous lizards cannot alter parental investment after their eggs are deposited, and therefore, in cases of fractional optimal clutch size, the next lower integral clutch size is selected with the remaining reproductive energy allocated to increased egg size. With other factors constant, eggs of smaller clutches will increase more in size than eggs of larger clutches when excess energy is divided among the eggs of a clutch. Secondly, unanticipated energy that may become available for reproduction during energy-rich years will similarly increase egg size a greater amount if divided among fewer eggs.     

Reproductive effort and reproductive nutrition of female desert tortoises: essential field methods

I used three innovative, nondestructive field methods (gas dilution,doubly labeled water and radiography) to measure individualenergy and water budgets of wild, female desert tortoises (Gopherusagassizii). With these budgets, I evaluated whether body reserveshelp females produce eggs independent of rainfall and food availability.Female desert tortoises used large seasonal and annual changesin metabolism and body water, protein and energy reserves tosurvive and produce eggs. Although lipid reserves are importantto female desert tortoises, nitrogen or crude protein appearsto be the primary limiting resource for producing eggs. By reducingmetabolic rates 90%, females conserved enough body reservesto produce eggs during extreme drought conditions; this is aneffective bet-hedging reproductive pattern in an extreme andunpredictable environment.     

Interrelations Among Water and Energy Relations of Reptilian Eggs, Embryos, and Hatchlings

Reptilian eggs previously categorized with respect to the flexibilityof eggshells appear to fall into two groups: endohydric eggsare those that are invested, by the female parent at the timeof oviposition, with all of the water necessary to completeembryogenesis; and ectohydric eggs which need to absorb waterfrom the nest medium tocomplete embryogenesis. Eggs of the Galapagosland iguana are unusual among most lepidosaurians by havingvery permeable parchment shells, but containing a large albumen(apparently serving as a reservoir of water for the embryo).It appears that the eggs of Galapagos land iguanas can exploitan endohydric habit without the rigid, impermeable shell seenin other endohydric eggs. This ability appears to be mediatedby two factors: eggs of Galapagos land iguanas are laid in drysoils which are essentially impermeable to water, and the verylarge eggs of land iguanas have a relatively small surface areatovolume ratio which results in a relatively small exchangeof water across the eggshell. It appears too that the waterrelations of Galapagos land iguana eggs will affect the energeticsof both the contained embryo and the subsequent hatchling. Withoutadequate water, land iguana eggs will produce hatchlings thatare both smaller and possess less fat to sustain thejuvenileduring the first year of life.     

The development of behavioral defenses: a mechanistic analysis of vulnerability in red-eyed tree frog hatchlings

I examined the development and effectiveness of behavioral defensesof red-eyed tree frog hatchlings, Agalychnis callidryas, against predatoryshrimp Macrobrachium americanum. Arboreal eggs of A. callidryashatch early if attacked by egg predators and later if undisturbed,producing tadpoles that enter the water at different developmentalstages. Older hatchlings survive better than young hatchlings withaquatic predators, including shrimp. Hatchlings respond to shrimpby both increasing activity and avoiding the bottom microhabitat.Older hatchlings are more active and, in the presence of shrimp,avoid the bottom more than young hatchlings. These ontogeneticchanges in behavior improve survival. Specifically, the likelihoodof fleeing from shrimp increases with hatchling age, and fleeingis an effective defense. In contrast to results from experimentswith odonates, immobility does not reduce risk of shrimp attack, thusthere is no trade-off between fleeing and motionless crypsis.Shrimp spend most of their time on the bottom, where attacksare more often successful. Avoidance of the bottom microhabitatby tadpoles therefore improves survival. Evasive maneuvers alsofunction in defense, but evasiveness does not change with age.Morphology may limit microhabitat use by younger hatchlings.Failure to flee may reflect unresponsiveness to disturbance,which would reduce unnecessarily early hatching and limit exposureof young A. callidryas to aquatic predators.     

Population dynamics of Aurelia aurita (Scyphozoa) from an isolated brackish lake, with particular reference to sexual reproduction

The annual cycle of abundance, growth and sexual reproductionof the scyphomedusa Aurelia aurita was examined over a 12 monthperiod in an isolated, shallow, brackish, man-made body of water:Horsea Lake, England. Strobilation started in December and ephyraewere present through June in varying numbers, suggesting a 7month period of near-continuous recruitment. Horsea Lake hasa dense A.aurita population, with the peak abundance of 24.9m^–3 occurring in mid-May. Medusae (>10 mm) were presentin the water column from March through January. Maximum belldiameter of 105 mm was observed in late September. However,medusa growth was very poor (G ranged between –0.03 and0.07 day^–1 over a 12 month period), and monthly mean belldiameters were typically <50 mm. For most of the year, theabundant A.aurita population was most likely severely food limitedas a result of a numerically and species-poor mesozooplanktoncommunity dominated by the calanoid copepods Acartia margalefiand Acartia tonsa. Nevertheless, the very small A.aurita medusaewere still able to attain sexual maturity and reproduce. Ripefemale medusae carrying fertilized eggs and planula larvae werefirst observed in May and June, although the main period ofplanula larva production was September-December. In November,all females were ripe, the smallest being 19–20 mm belldiameter. At both Horsea Lake and a nearby productive estuary,Southampton Water, planula larva production increased linearlywith wet weight, although compared with the larger A.auritamedusae from Southampton Water, reproductive output at HorseaLake was low. Aurelia aurita in Horsea Lake showed plasticityin its population characteristics in response to environmentalconditions, with both fecundity and size to maturity varyingon a seasonal basis. Medusae appeared to partition the availablefood resources into either somatic growth when food was abundantor reproductive effort when food was scarce.     

Some Aspects of the Nesting Behavior and Reproductive Biology of Sea Turtles

Basic reproductive data from 21 green turtle (Chelonia mydas),8 leatherback (Dermochelys coriacea), 7 hawksbill (Eretmochelysimbricata), 7 olive ridley (Lepidochelys olivacea),6 loggerhead(Caretta caretta), 1 Kemp's ridley (Lepidochelys kempi), and1 flatback (Chelonia depressa) populations are provided. Someintraspecific and interspecific relationships between size ofnester and clutch, egg size and hatchling size are analyzed.Measurements of reproductive rates (=numbers of hatchlings perfemale per year) in 11 populations varied from 35 to 200 inan olive ridley and loggerhead colony, respectively. Nestingbehavior of each species is described in terms of type of nestingemergence and time spent on the nesting beach (=chelonery).The relatively large number of yolkless eggs laid by many leatherbacksand by some hawksbills invites further study. Some aspects ofsea turtle nesting behavior and reproduction are compared tothose of other chelonians.     

PRELIMINARY INVESTIGATIONS OF THE ECOLOGY OF THE INTERTIDAL PREDATORY GASTROPOD LEPSIELLA VINOSA (LAMARCK) (GASTROPODA MURICIDAE)

Lepsiella vinosa\ (Lamarck), a common intertidal predatory gastropod,was studied in two zones on an exposed rocky shore in Victoria(Australia). Those from the Mussel Zone in the mid-shore primarilyate one species of mussel and had a faster rate of energy consumptionthan those from the Littorinid Zone in the high-shore, whichmainly ate one species of littorinid gastropod. Shell length,growth rate and size-specific body weight of L. vinosa wereall significantly greater in the Mussel Zone. Egg capsules ofL. vinosa from the Mussel Zone contained significantly moreeggs and more potential hatchlings per capsule than those fromthe Littorinid Zone although there were no significant differencesin the sizes of eggs or hatchlings between zones. These differencesbetween the two zones were correlated to the greater consumptionof energy by L. vinosa in the Mussel Zone and were discussedin relation to the absence of dispersive larvae in this species ¹Present address: Department of Zoology, Monash University,Clayton, Victoria, 3168, Australia ²Present address: School of Biological Sciences, Carslaw Building,F07, University of Sydney, N.S.W., 2006, Australia. Addresseefor reprints. (Received 2 June 1987;     

Effects of parasitic infection and reproduction on corticosterone plasma levels in Galápagos land iguanas,Conolophus marthae and C. subcristatus

In vertebrates, one main feature of stress response is the release of glucocorticoids (corticosterone in reptiles), steroid hormones whose synthesis is regulated by the hypothalamic–pituitary–adrenal axis (HPA). In the Galápagos Islands, populations of land iguanas are differentially impacted by a tick‐transmitted apicomplexan hemoparasite of genus Hepatozoon, which could cause diseases and ultimately reduce fitness. Using competitive enzyme‐linked immunosorbent assays (ELISA), we examined baseline plasma corticosterone levels of two syntopic and highly parasitized populations of the land iguana species Conolophus marthae and C. subcristatus in Wolf volcano (Isabela Island). We also used a poorly parasitized population of C. subcristatus from the same island (Bahia Urbina) as a reference. To better interpret the observed glucocorticoids patterns, we simultaneously performed the count of white blood cells (WBCs) in all individuals and investigated the reproductive status of females. We did not find evidence in support of either a positive or negative relationship between the tick load, hemoparasite infection, and glucocorticoid plasma concentration in C. marthae and C. subcristatus at Wolf volcano. The comparison between parasitized and non‐parasitized sites (V. Wolf and Bahia Urbina) would instead suggest an inverse relationship between corticosterone and parasites. Our findings support association between corticosterone plasma levels and reproduction.     

Seasonal and fine-scale spatial variations in egg production and triacylglycerol content of the copepod Acartia tonsa in a river-dominated estuary and its coastal plume

We measured egg production rates of the estuarine calanoid copepodAcartia tonsa in Mobile Bay, an estuary in the northern Gulfof Mexico. Two stations were sampled approximately monthly,one at the mouth of the bay and the other just beyond the mouthin the salinity front between bay and coastal waters. Over thewhole year, temperature was the most important environmentalvariable controlling egg production. Rates increased with temperatureup to 30°C and 140 eggs female^–1 day^–1. We foundno evidence of food limitation. There was no correlation betweenegg production and phytoplankton abundance, nor increased eggproduction in response to supplements of phytoplankton addedto natural food, suggesting that non-phytoplankton food wasimportant in the diet. At the highest egg production rates,the amount of the storage lipid triacylglycerol (TAG) in adultfemales was greatly diminished, to <50 ng female^–1.This suggests that lipids in the diet can be very tightly coupledto egg production. Both egg production and TAG content of femalesshowed significant variability on spatial scales of 3–15km, especially in relation to the salinity front separat ingwater outwelling from the bay from open coastal water. For organismsthat are using copepods and their eggs as food, this variabilitywould result in a heterogeneous food environment, both in termsof the abundance of food and its nutritional content.     

Experimental demonstration of the insurance value of extra eggs in an obligately siblicidal seabird

A variety of organisms regularly produce more offspring thanthey raise. Despite the apparent energetic waste of such areproductive tactic, overproduction may be favored by naturalselection in some cases. One such case is when surplus offspringcan serve as replacements, or insurance, for failed siblings.We tested the Insurance Egg Hypothesis (IEH) as an explanationfor the overproduction of offspring in an obligately siblicidal seabird, the Nazca booby (Sula grant)i, which fledges a maximumof one nestling regardless of its clutch size. We manipulatedclutch sizes within the range of natural variation encounteredin this species (one-two eggs). The IEH predicts that parentswith two-egg clutches should have higher reproductive successthan those with one-egg clutches because the second egg canprovide a nestling when the first egg fails to hatch, or when the first chick dies young. Consistent with the IEH, naturalone-egg clutches that were enlarged to two eggs produced morehatchlings and fledglings than control one-egg clutches did,and natural two-egg clutches that were reduced to one egg producedfewer hatchlings and fledglings than control two-egg clutchesdid. We also evaluated aspects of the Individual Optimization Hypothesis, which proposes that individual optimal clutch sizesdiffer, as an explanation for clutch size variation in thisspecies. In Nazca boobies, selection driven by replacementvalue appears to favor clutches larger than one even thoughfinal brood size is invariably one. One-egg clutches may be produced by parents experiencing some proximate limitation,such as a lack of food.     

Reproductive pattern of Brachionus calyciflorus Pallas at different food concentrations

Laboratory populations of Brachionus calyciflorus were grownat different food levels, to determine whether B.calyafloruswas capable of varying its reproductive pattern, according tothe concentration of available food to maintain a high rateof population growth The volume of eggs borne by females wasmeasured, and the carbohydrate content of the animals was analysed.When food was abundant, egg volume and carbohydrate contentwere low Since small neonates can easily become adults becauseof the good food conditions, B calyciflorus utilized its energyto increase the number of offspring At low food concentrations,there was an important increase in egg volume and carbohydratecontent As egg numbers decreased, then B calyciflorus then appearedto use its energy to increase neonate size. Tins tendency wasmaintained down to a threshold concentration, below which eggvolume and carbohydrate content diminished again due to insufficientfood     

Molecular data exclude current hybridization between iguanas <Emphasis Type="Italic">Conolophus marthae</Emphasis> and <Emphasis Type="Italic">C. subcristatus</Emphasis> on Wolf Volcano (Galápagos Islands)

Natural hybridization may influence population fitness and responsiveness to natural selection, in particular in oceanic island systems. In previous studies, interspecific hybridization was detected between the Galápagos iguana species Amblyrhynchus cristatus and Conolophus subcristatus. Further, possible hybridization was also suggested to occur between C. subcristatus and C. marthae at Wolf Volcano on Isabela Island. In this work, we investigated the level of hybridization between C. subcristatus and C. marthae using a large set of microsatellite markers. Results indicated strong differentiation between species and, while we cannot rule out hybridization in the past, there is no evidence of ongoing hybridization between C. marthae and C. subcristatus. These findings have great importance for the design of management actions and conservation plans, in particular for the purposes of a head start program. However, because potential for hybridization may change under different environmental and demographic conditions, genetic characterization of newly marked individuals of C. marthae and C. subcristatus in Wolf Volcano should not be interrupted.     

A Suite of Adaptations for Intertidal Spawning

Salt marshes and similar tide-dominated habitats present anunusual challenge for reproduction of resident aquatic organisms.Strong currents, siltation and hypoxia can potentially contributeto reproductive failure through mortality of the eggs or flushingof the eggs and larvae from the habitat. Fundulus heteroclitus,a small brackish water killifish, is a common resident of tidalmarshes along the east coast of North America from Newfoundlandto Florida. The reproductive strategy of this and related speciesis based on aerial incubation of eggs in the high intertidalzone. The eggs are resistant to desiccation and, when fullydeveloped, hatch on immersion. Copulatory behavior and anatomyof accessory reproductive structures are adapted to placementof eggs in protected incubation sites. The gonads of both malesand females mature rhythmically with an endogenous circasemilunarperiod, which is synchronized with the "spring" tides of newand full moons. Spawning occurs on high tides. Embryos developin 9–15 days, and usually hatch on the succeeding springtide series. Reproductive cyclicity in F. heteroclitus and relatedfishes ensures that spawning fish will have access to the highintertidal zone, thereby permitting aerial incubation of eggs.     

Erfahrungsbericht über die Haltung und deutsche Erstzucht der Borneo-Flussschildkröte (Orlitia borneensis Gray, 1873) im Zoo Dresden

Dresden Zoo bred successfully the Malaysian giant turtle (Orlitia borneensis) in summer 2012. This was the first successful breeding of this species in Germany.Little is known about biology and behaviour of this large river turtle and keeping and especially breeding of this endangered species in captivity is a rarity. In order to create optimal breeding conditions Dresden Zoo rebuilt an enclosure for the turtles in 2010. An area with soil and sand was built for the expected egg deposition. After arranged matings one female dug a nest on this area and buried her eggs. Nine eggs were secured and transferred into an incubator in a box filled with a 1:1 mixture of vermiculite and water. The average temperature was 29 °C. After problems with the temperature regulation the damaged incubator had to be replaced. Because of an estimated incubation period of 3–4 months, one egg was opened on day 127 of incubation. A live hatchling with a big yolk sac was fetched. Because of the non-reabsorbed yolk sac the hatchling was further incubated. On day 154 of incubation all eggs were manually opened and the hatchlings were fetched. All of these hatchlings showed a non-reabsorbed yolk sac and were incubated onwards in a box with wet paper towel until the yolk sac was completely reabsorbed. After that the hatchlings were housed solitarily in a box with water of approximately 4 cm height and a small land area. Two days after housing food was offered for the first time. All hatchlings accepted the offered food consisting of herbal as well as of animal products and later turtle pellets and self-made turtle jelly.Though little is known about breeding this species, the breeding success of Dresden Zoo demonstrates a possible approach to this topic. But there are still things to optimize. For example the manual hatching is something that should be avoided in future. Fertilization and hatching rate of 100% are promising and up to date eight out of nine hatchlings are still alive.     

Phase-specific responses to different qualities of food in the desert locust, Schistocerca gregaria: developmental, morphological and reproductive characteristics

Solitarious female adults are known to produce smaller hatchlings than those produced by gregarious adults of the desert locust, Schistocerca gregaria. This study investigated developmental, morphological and reproductive responses to different qualities of food in hatchlings of different phases. Mortality was higher, the duration of nymphal development longer and adult body weight lighter with a low-quality food than a high-quality food. Gregarious hatchlings showed better survivorship, grew faster and became larger adults than did solitarious ones. The incidence of locusts exhibiting extra molting, which was typically observed in the solitarious phase, was dramatically increased when a low-quality food was given to the solitarious hatchlings. Low-quality food caused locusts to shift morphometric ratios toward the values typical of gregarious forms; smaller F/C (hind femur length/maximum head width) and larger E/F (elytra length/hind femur length). Solitarious hatchlings grown at either high- or low-quality foods and then given high-quality food after adult emergence revealed that food qualities during the nymphal stage influence their progeny quality and quantity via adult body size that influenced reproductive performance. Female adults showed an overshooting response to a shift from low- to high-quality food by increasing egg production that was specific to body size. This study may suggest that gregarious hatchlings are better adapted to adverse food conditions than solitarious counterparts and extra molting is induced even among gregarious hatchlings under poor food conditions.     

ADAPTATIONS FOR COLD WATER SPAWNING IN LOLIGINID SQUID: LOLIGO GAHI IN FALKLAND WATERS

Inshore spawning sites of the cold water squid Loligo gahiwere found in the waters of East Falkland (Southwest Atlantic),where there is a major fishery based on this species. Egg massesoccurred in algal beds, often at the outer (seaward) edge, with ambientwater temperatures of 6.5-90C and salinity 33.75- 33.58. They wereattached to the stipes of the kelp algae Lessonia spp. and Macrocystispyrifera from 0.5 m to 2.5 m off the bottom at 8-20 m depths.The overall density of egg masses was low. The egg mass is abundle of elongated gelatinous translucent capsules with eachcapsule firmly attached to the kelp stipe at its basal end.The capsules are mainly 50-60 mm in length and contain an averageof 70 fertilized eggs. Sampled egg masses consisted of 4-161 capsulesand from 138 to 11,487 eggs. Large egg masses (. 50 capsules) wereapparently formed by several females at different times, as embryosin different capsules were at various stages of development.Eggs laid in winter are significantly larger than those laidin summer. In comparison with tropical and temperate Loligo spp.L. gahi have short egg capsules containing a small number of eggs,but the eggs (2.2-2.5 mm diameter) and hatchlings (3.1-3.4 mm mantlelength) are large. These are probable adaptations for cold waterspawning and development. (Received 30 March 2000; accepted 5 June 2000)     

Natural Selection of Optimal Reproductive Tactics

Acting through differential reproductive success, natural selectionhas produced a great diversity of existing reproductive tactics,each of which presumably corresponds to a local optimum thatmaximizes an individual organism's lifetime reproductive successin its particular environment. A body of theory on so-calledreproductive "strategies" has yet to be adequately related toan independent theoretical framework on optimal foraging tactics.Some of the possible interactions and constraints between ananimal's input of matter and energy via foraging and its outputin offspring using these same materials are briefly considered.For example, storage and utilization of lipids allow an organismto gather and sequester matter and energy during a period thatis not suitable for successful reproduction, but enable theorganism to expend those materials at a later, more satisfactorytime. Such interactions between foraging and reproduction leadto a sort of temporal integration, which greatly complicatesestimation of reproductive effort (current investment in seed,eggs, or progeny) in variable environments. An optimal reproductivetactic maximizes an individual's reproductive value (the sumof all present plus the expected probable number of all futureoffspring) at every age. Reproductive effort should vary inverselywith residual reproductive value (expectation of future offspring);moreover, the precise form of the trade-off between presentoffspring versus future progeny, which is itself sensitive toa multitude of environmental influences including resource availabilityand the immediate environmental conditions for reproductionand survival, dictates the optimal tactic at any given age.Simple graphical models of optimal reproductive tactics arepresented and discussed. Finally, some promising directionsfor future work, as well as certain potential difficulties,are noted.     

A Quantitative Study of Environmental Factors Influencing the Seasonal Onset of Reproductive Behaviour in the South American Apple-snail Pomacea canaliculata (Gastropoda: Ampullariidae)

Two laboratory experiments were carried out on sets of winter(inactive) pairs of Pomacea canaliculata (Lamarck), one to studythe influence of water temperature (either 18°C or 25°C,corresponding to late winter and summer temperatures in Mendoza, respectively)and day length (either 10 h light/day or 14 h light/day, correspondingto the shortest and the longest day of the year in Mendoza,respectively), and the other to determine the effects of foodavailability (ad libitum feeding vs. restriction to 25% of thead libitum requirements) on the frequency of copulation andspawning, on spawn measurements (number and volume of eggs,and spawn volume), and on an index of the reproductive effort.Animals in all experimental groups were observed during 4 weeks,after seven days of acclimation to the experimental aquaria(under low water temperature and short photoperiod). Low watertemperatures induced a lesser and later activation of copulationand spawning than that induced by warm temperatures. Day lengthwas without effect on both behaviours. Both the frequency ofspawning and the reproductive effort index decreased under restrictedfeeding, without altering the spawn measurements. The latencyperiods for both copulatory and spawning behaviours were similarin both ad libitum and restrictedly fed groups. We concludethat water temperature may be the critical factor that causesthe seasonal onset of copulatory and spawning behaviour in theseapple-snails. However, food availability may also be a determiningfactor, mainly to trigger spawning activity. These results suggestthat the factors that control the seasonal onset of the sexualactivities in Pomacea canaliculata are similar to those thatcontrol the seasonal arrest, thereby establishing the annualpattern of reproduction in this species. (Received 26 January 1998; accepted 23 July 1998)     

Fruit abundance may fine-tune timing of reproduction of the Chilean Elaenia (Elaenia chilensis), a long-distance migratory bird in South America

Timing of reproduction has a great impact on the breeding success of birds because a mismatch with the moment when environmental conditions are warm or when food is most plentiful can reduce nestling survival and increase the energetic cost of parental care. Consequently, birds synchronize gonadal maturation with the most favourable environmental conditions, using photoperiod changes throughout the year as an initial proximal cue. Additionally, non-photic cues, such as temperature and food abundance, may be necessary to fine-tune reproductive timing. However, the influence of non-photic cues on finely tuning reproductive timing is not yet fully understood for migratory birds. Here, we evaluate how much non-photic cues influence the reproductive timing of the Chilean Elaenia Elaenia chilensis, a long-distance migrant that reproduces in the Andean–Patagonian Forest. We assessed associations of mean temperature, ripe fruit and arthropod abundances with the number of nests in the laying period, and also with the number of nests with hatchlings. In both analyses we used cross-correlations and partial least squares path modelling. Mean temperature was not consistently associated with the breeding phenology of Chilean Elaenias. The increase in number of nests in the laying period was preceded by the increase in caterpillar abundance and coincided with the increase in ripe fruit abundance. The timing of nests with hatchlings matched with the timing of highest ripe fruit abundance. Both types of food could contribute to the beginning of reproduction of birds and be used as proximal cues by Chilean Elaenias. Ripe fruits would also be beneficial for nestling growth because parents feed them with fruits, and might potentially play an ultimate role in reproduction. Because ripe fruit abundance was related to the egg-laying and hatching stages, it may be the main cue used by Chilean Elaenias to fine-tune reproductive timing. These findings allow advances in our understanding of the importance of non-photic cues in the reproductive phenology of migratory birds and also generalize our knowledge among regions and taxa, as most studies on this topic focus on the Northern Hemisphere.     

Functional response and food selection of the water flea, Bosmina longispina

The functional response and the feeding behaviour of Bosminalongispina in relation to varying food concentrations were investigatedunder laboratory conditions using radioactively labelled Scenedcsmusacutus and different sized fluorescent latex beads to measureclearance rates and size selectivity. Bosmina longispina reducedfeeding activity at low concentrations of food, having a sigmoidfunctional response. Particles of 5.18 µm were filteredmuch more efficiently than both 1.04- and 0.25-µm particles,and the selectivity of large particles increased with increasingfiltering rates. Scenedesmus acutus was filtered at approximatelythe same rate as 5.18-µm latex beads. The increased selectivityat high filtering rates is explained as an adjustment in thefiltering apparatus to allow for greater water flow. Both thesefeeding responses would tend to reduce energy expenditure insituations when energy intake is low.