Interhabitat and instream movements of large Atlantic salmon parr in a Newfoundland watershed in winter

Radio‐telemetry was used to investigate movement of large, mainly mature male (80%) Atlantic salmon Salmo salar parr in Stoney River, Newfoundland during early winter (November; water temperature 6·0 ± 0·1° C) and mid‐winter (January to February; 0·8 ± 0·0° C). Site fidelity of parr in early winter was low. Parr moved between fluvial and lacustrine habitats and were active throughout the diel cycle. Parr caught in fluvial habitats in mid‐winter were smaller and younger than parr caught in early winter. Site fidelity of parr in mid‐winter was greater than in early winter. Parr in mid‐winter moved between fluvial and adjacent small lacustrine habitats, but avoided a larger pond inhabited by large piscivorous fishes. Instream movement rates in mid‐winter were lower than in early winter and occurred primarily during hours of darkness (dawn, dusk and night). Fluvial habitats were relatively stable and ice‐free throughout the study periods. These results suggested that large Atlantic salmon parr utilize a variety of habitats and remain active throughout the winter, even under stable environmental conditions.     

The effect of reduced temperature and salinity on the blood physiology of juvenile Atlantic cod

The osmolality and ionic composition of the blood of juvenile Atlantic cod Gadus morhua and their response to conditions of reduced temperature and salinity in summer‐ and winter‐acclimated individuals was investigated. Haematocrit percentage was relatively stable throughout the experimental procedures. Summer‐acclimated juvenile Atlantic cod had higher plasma osmolality than winter‐acclimated fish in ambient conditions. Plasma Na⁺ levels were, however, higher in winter conditions, while Cl⁻ did not vary between seasons. Temperature reduction (12, 9 and 6° C in summer and to 6 and 4° C in winter) induced a significant response in plasma osmolality and Na⁺ levels in summer, but only in Na⁺ levels in winter‐acclimated fish. A pronounced effect was seen in the summer 6° C treatment. Salinity treatments (24, 16 and 8) had a significant effect on almost all the variables in both summer and winter and resulted generally in dilution of ionic and osmotic concentrations of the plasma. This effect was pronounced in the lowest temperature treatments, with the greatest reduction observed in the summer 6° C treatment. This could suggest that winter‐acclimated fish are physiologically adapted to cope with lower seawater temperatures as opposed to summer‐acclimated fish.     

Physiological responses in Nile tilapia exposed to different photoperiod regimes

After conditioning Nile tilapia Oreochromis niloticus for 2 weeks, the photoperiod regime of 12 tanks of fish was changed to a 6L : 6D photoperiod while 12 further tanks were retained on the conditioning photoperiod regime (12L : 12D). Blood samples were collected 3 days (first sampling) and 3 months (second sampling) after changing the photoperiod regime. Blood was collected at 6 h intervals from both photoperiod regimes (1000, 1600, 2200 and 0400 hours). At the first sampling time, fish in the 6L : 6D had significantly higher cortisol both in the light and dark phases than levels in fish in the 12L : 12D photoperiod. At the second sampling time, the levels were significantly higher only in the light phase. The levels of cortisol, glucose and Cl⁻ in fish exposed to the 6L : 6D photoperiod, however, were far lower than those of acute stress‐induced levels observed in fish exposed to a stress experiment. Furthermore, there were no significant differences in overall values of all the variables between the photoperiod regimes at the second sampling time. This indicated that the fish exposed to the 6L : 6D photoperiod were not chronically stressed. Significantly higher blood lymphocyte counts were observed in fish exposed to the 6L : 6D compared to those of the 12L : 12D photoperiod during the light phase at the second sampling time. Other variables (glucose, Cl⁻, haematocrit and neutrophil) did not show a significant difference between the treatments at either sampling time. These results demonstrated that the artificial photoperiod regime did not cause a significant acute or chronic stress response in Nile tilapia.     

Effects of temperature and delayed initial feeding on the survival and growth of Japanese flounder larvae

The effects of the timing of initial feeding (0, 1, 2, 3 and 4 days after yolk exhaustion) and temperature (15, 18 and 21° C) on the point‐of‐no‐return (PNR), survival and growth of laboratory‐reared Japanese flounder Paralichthys olivaceus larvae were studied under controlled conditions. The larvae reached PNR on 7·7, 5·2 and 4·2 days‐post‐hatching (dph) at 15, 18 and 21° C, respectively. At each temperature, larval growth did not differ significantly among the delayed initial feedings 1 day before PNR but decreased significantly in larvae first fed after that. In the treatments where initial feeding was equally delayed, larvae grew significantly faster at 18 and 21° C than at 15° C. The larvae survived apparently better at 15 and 18° C than at 21° C when initial feeding was equally delayed. At each temperature, survival of the larvae first fed before PNR did not differ noticeably, while delayed initial feeding after that apparently reduced their survival. These results indicated that there existed a negatively temperature‐dependent PNR in the Japanese flounder larvae. Survival and growth of the larvae strongly depended on temperature as well as the timing of initial feeding. High temperature accelerated the yolk exhaustion and growth of the larvae and thus reduced their starvation tolerance and survival. To avoid potential starvation mortality and obtain good growth, the Japanese flounder larvae must establish successful initial feeding within 2 days after yolk exhaustion at 15° C and within 1 day at both 18 and 21° C.     

Implications of Chaoborus pupation and ecdysis in cold water

1. Cold water acted differently to delay and lengthen the pupation period for the larvae of two species of the zooplankton predator Chaoborus (Diptera: Chaoboridae). During Chaoborus pupation, the zooplankton community is released from predation, while the dark-coloured Chaoborus pupae are more susceptible to their own predators.
2. Fourth instar larvae of Chaoborus americanus and C. trivittatus , collected from an oligotrophic lake, were reared individually at 5 °C in the dark. Chaoborus americanus was also reared at 9 and 12 °C under spring photoperiod conditions (L : D, 16 : 8 h). Individuals were observed through pupation to emergence (ecdysis) or death.
3.  Chaoborus americanus pupated at 5, 9 and 12 °C with substantial emergence only at 12 °C. In comparison, C. trivittatus emerged at 5 °C. Light was not a necessary cue for pupation and ecdysis, contrary to previous reports. Cold water delayed the onset and lengthened and increased the variability of the duration of pupation.
4. In Shirley Lake, C. americanus pupated in late June–early July while C. trivittatus pupated first in April and again in June–July.
5.  Chaoborus americanus pupae needed a temperature cue to complete ecdysis. The ecdysis temperature threshold helps to explain the difference in pupation timing, and the geographical distribution, of C. americanus and its relatively inflexible life history contrasted with C. trivittatus . Delayed predator pupation in years with low spring temperature can affect the community dynamics of the prey.     

Individual feeding success of juvenile perch is consistent over time in aquaria and under farming conditions

Juvenile (0+ year) perch Perca fluviatilis , held in tanks (1 m³) for 8 months under constant temperature (17° C) and light (12L : 12D) conditions, were weighed monthly. Individually marked fish from the tanks were placed in aquaria in groups of four and tested for feeding success, assessed as individual share of a group meal in three identical short‐term aquarium experiments separated in time (January, May and June). The groups consisted of the same individuals in each of the three experiments. In tanks, growth (thermal growth coefficient, G _T) was used as a measurement of feeding success. Individual G _T in tanks was consistent over time, and individual share of a group meal in aquaria was consistent between consecutive months. There was no connection between individual feeding success in aquaria and G _T in tanks in May and June, and in January the factors were negatively correlated. The condition factor at the start of aquarium experiments and feeding success in aquaria were negatively correlated in June and tended to be so also in May. Boldness in aquaria was negatively correlated with growth in tanks. Thus, individuals that were successful in one environment seemed to be less successful in the other. There was a seasonal change in G _T, with an increase from March to April and from April to June despite constant day length and temperature.     

Effect of temperature on life table parameters of Podisus nigrispinus (Het., Pentatomidae) fed with Alabama argillacea (Lep., Noctuidae) larvae

Abstract: The influence of temperature on life table parameters of Podisus nigrispinus (Dallas) (Het., Pentatomidae) fed with Alabama argillacea (Hübner) (Lep., Noctuidae) larvae was studied. This predator was kept at constant temperatures of 20, 23, 25, 28, 30 and 33±0.2°C, at relative humidity of 60±10% and photoperiod of L : D 14 : 10. Gross (GRR) and net ( R ₀) reproductive rates of P. nigrispinus ranged from 1.6 to 366.6 and from 0.02 to 189.5 females/female at temperatures of 33 and 28°C, respectively; generation time ( T  ) ranged from 33.3 (33°C) to 85.5 (20°C) days; doubling time ( D ) from 0.82 (33°C) to 17.8 (20°C) days; intrinsic rate of increase ( r _m ) from −0.13 (33°C) to 0.12 (28°C) per day; and the finite rate of increase ( λ ) from 0.88 (33°C) to 1.12 (28°C) females/female added to the population per day. The ideal age to release P. nigrispinus should be when this predator presents higher reproductive values (VR _x ); that is, its adults are about 7 days old, independent of prevailing temperature. Population growth of P. nigrispinus was affected by temperature with maximum numerical response between 28 and 30°C. The negative population growth shown at 33°C may not occur in natural conditions due to milder microclimate in the cotton agroecosystem and due to oscillations of temperature in the course of the day.     

Climatic and biogeographical associations of southern African dung beetles (Coleoptera: Scarabaeidae s. str.)

Climatic and biogeographical associations of southern African dung beetles (Scarabaeinae, Coprinae) were analysed from a collection amassed between 1971 and 1986. Endemism to Africa south of 15°S was much greater in southwesterly climates (winter rainfall, bimodal spring/autumn rainfall, arid late summer rainfall) than to the north‐east in the moist, mid‐summer rainfall region. Major biogeographical groups centred to the south‐west comprised predominantly southern African endemics, Western/Eastern Cape coast, Karoo, Karoo/Namib, northern Namibia and the south‐western Kalahari. Biogeographical groups centred on the south‐eastern highlands and the subtropical east coast (mid‐summer rainfall) also comprised predominantly southern African endemics. All other major groups centred to the north‐east in the mid‐summer rainfall region comprised predominantly species with widespread tropical biogeographical affiliations, pan‐southern Africa but centred in the east, pan‐mid‐summer rainfall region, eastern mid‐summer rainfall region, tropical east Zimbabwe/central Moçambique, subtropical/tropical game reserves (non‐ruminant dung specialists). There were cross‐climatic differences in taxonomic composition of the fauna. Within the winter rainfall region, percentage species composition of Scarabaeinae was greater whereas that of the coprine tribe, Onthophagini, was lower than within the other three climatic regions. Percentage species richness of most other tribes of Coprinae differed little between most climates but that of Scarabaeinae declined from west to east (Canthonini, Scarabaeini), east to west (Sisyphini) or to either side of the late summer rainfall region (Gymnopleurini).     

Hsp70 is not a sensitive indicator of thermal limitation in Gadus morhua

The levels of heat‐shock proteins of the 70 kDa family (Hsp70s) were measured in different soft tissues of Atlantic cod Gadus morhua from different locations and after exposure to various thermal conditions: acute temperature increments (1° C day⁻¹), mid‐term (73 days at 4–15° C) and long‐term thermal acclimation (278 days at 8–15° C), and seasonal and latitudinal temperature variations (field samples). Tissue specific distribution patterns of Hsp70s were observed: liver > gills > red blood cells > brain > white muscle. Thus, different tissues may have required different levels of protection by Hsp70s, and possibly this was related to the rate of protein synthesis. There were no differences in tissue Hsp70s between Arctic cod populations (Arctic, i.e . Barents and White Seas, Norwegian coast, and North or Baltic Seas). No changes in Hsp70s levels were observed in response to temperature variation of any intensity (acute fluctuation or seasonal and latitudinal) within the range of physiological temperatures (4–15° C) in wild and laboratory Atlantic cod. This confirms previous observations that changes in Hsp70 caused by such temperature variation are often small in fishes. Probably, the constitutive level of Hsp70s in Atlantic cod was high enough to overcome potentially harmful effects of temperature variations within the physiological range. A suppressing effect of high temperature (15° C) has already been observed at a systematic level (as reduced rate of somatic growth), whereas it is not reflected in modified Hsp70s. Therefore, Hsp70s apparently played a secondary role in defining thermal tolerance limits in Atlantic cod. These conclusions are in line with a recent concept of thermal tolerance which indicated that the first line of thermal limitation in the cold and warm is a loss in aerobic scope.     

Effects of different photoperiods and wavelengths of light on the life-history traits of an aphidophagous ladybird, Coelophora saucia (Mulsant)

Abstract:  The influence of three photoperiods, viz. short day [8 : 16 h; light : dark (L : D)], long day (16 : 8 h; L : D) and continuous light (24 : 0 h; L : D) and four wavelengths of light, viz. white (control), yellow, blue and red on pre-imaginal development and reproductive performance of a ladybird, Coelophora (= Lemnia ) saucia (Mulsant) (Col., Coccinellidae) have been investigated under laboratory conditions. Long-day photoperiod and white light resulted in low immature stage mortality. Total larval period was longest under short-day and red-light conditions. Females kept at long-day photoperiod and under white light showed better reproductive performance than those placed under other photoperiods and wavelengths.     

Daily progeny production and thermal influence on development and adult longevity of the leafminer parasitoid, Gronotoma micromorpha (Hym., Eucoilidae)

Abstract:  To evaluate the potential of the parasitoid Gronotoma micromorpha (Perkins) as a biological control agent for the serpentine leafminer Liriomyza trifolii (Burgess) in greenhouses, we determined daily progeny production and thermal influence on both total development (oviposition to adult emergence) and adult longevity of this wasp in the laboratory in the host L. trifolii . The mean total number of progeny produced was 75.6 per female at 25°C under a 15-h light/9-h dark (15L : 9D) photoregime. The developmental rate of G. micromorpha significantly correlated with constant temperature between 18 and 30°C. The lower thermal threshold and thermal constant for total development of this wasp were 11.7°C and 333.3 heat degree-days, respectively. The results indicate that adult female G. micromorpha do not oviposit at 15°C and that the lower threshold for oviposition is approximately 18°C. In heated greenhouses in Japan, leafminers and their parasitoids are exposed to both high temperatures and a short photoregime from late autumn to winter, but these conditions (25°C, 10L : 14D) did not significantly affect the total development of G. micromorpha . When wasps were not exposed to hosts, the mean adult longevity at 15 or 20°C was significantly longer than that at 25°C. When wasps were allowed to oviposit into hosts at 25°C, the mean adult longevity was significantly longer than when wasps were not exposed to hosts. As adult female G. micromorpha do not feed on hosts and are pro-ovigenic, suppression of oviposition probably decreased adult longevity. The biological traits of G. micromorpha elucidated by this and previous studies indicate that this wasp is suitable as a biological control agent for L. trifolii in greenhouses.     

Effects of temperature on the development and survival of an endangered butterfly, Shijimiaeoides divinus barine (Leech) (Lepidoptera: Lycaenidae)

The effects of temperature on the development and survival of Shijimiaeoides divinus barine were examined in the laboratory in 2008. The eggs and larvae were reared at temperatures of 15, 17.5, 20, 25, 30 and 35°C with a long-day photoperiod of 16 h light : 8 h dark (16L : 8D). The highest hatchability of eggs was 88.0% at 20°C, but hatchability at high temperatures of 30 and 35°C was 30 and 0%, respectively. The lowest and highest survival rates from the first to third instar were 18.8% at 15°C and 76.9% at 20°C. Few deaths were observed after the fourth instar. The shortest developmental periods of the eggs and larvae were 4.0 and 15.8 days at 30°C, and the durations of the egg and larval stages increased significantly as the temperature decreased. The developmental zero and thermal constants were 9.6°C and 82.6 degree–days for the egg stage, and 10.7°C and 306.8 degree–days for the larval stage. The developmental period of the natural population of S. divinus barine in Azumino City, Nagano Prefecture was calculated using the developmental zero, thermal constants and Azumino City temperature data.     

Ontogenetic changes in temperature preference of Atlantic cod

Final thermal preferendum ( T ) experiments were conducted in a horizontal thermal gradient tank from the beginning of August 2001 to mid‐November 2001 using Atlantic cod Gadus morhua from 6·5 to 79·0 cm fork length ( L _F). The value of T varied significantly ( P  < 0·005) with L _F( T  = 7·23–0·054 L _F), with smaller (younger) fish choosing higher temperatures than larger (older) fish. The preferendum varied from 6·9° C for fish of 6·5 cm to 3·0° C for those of 79·0 cm. Experiments comparing fish positions in the gradient tank between thermal gradients of 0·5–11·0 and 4·5–14·5° C demonstrated that fish positions were determined by temperature selection instead of undesirable tank effects. This study is the first to demonstrate the effect of ontogeny on temperature preferences of a marine fish species.     

Effects of photoperiod and temperature on the development and diapause of the bark beetle Ips typographus

Abstract:  Diapause was induced in a Central European population of Ips typographus grown at 20°C when the day length decreased below 16 h [50% diapause incidence occurred in the 14.7:9.3 h L:D (light:dark) regime]. The non-diapausing adults fed on days 2–6 and 10–14 after the ecdysis and swarmed after the second feeding bout with chorionated eggs in the ovaries and sperm in the spermiducts. Neither gonads nor the flight muscles matured and no swarming occurred in the diapausing adults. The development from egg to adult took about 34 days in both 18:6 h (no diapause) and 12:12 h L:D (diapause) regimes, but it was extended by up to 30% without diapause induction when only larvae or pupae were exposed to L:D 12:12 h. Diapause was induced in insects reared at L:D 12:12 h through the last larval and the pupal instars and/or in the adult stage. Temperature ≥ 23°C prevented diapause induction at L:D 12:12 h but diapause occurred at L:D 14:10 h associated with 26:6°C thermoperiod. The effect of thermoperiods on the developmental rate requires further research. Exposure of the non-diapausing adults to 5°C for several days blocked feeding and evoked a diapause-like state, whereas diapausing adults fed and their gonads slowly developed at this temperature. Diapausing adults exposed in forest to low night temperatures and transferred in October to 20°C readily reproduced at 18:6, but not 12:12 h L:D photoperiods. After 2-months at 5°C and darkness, they became insensitive to the photoperiod, matured and most of them also swarmed at 20°C in the 12:12 h L:D regime. In a Scandinavian population, diapause occurred at 18:6 h L:D and was terminated either by exposure to 5°C or by very long photoperiod (L:D 20:4 h) combined with high temperature (23°C).     

Patterns of metamorphosis in summer flounder, Paralichthys dentatus

Summer flounder, Paralichthys dentatus , spawn over the continental shelf off the east coast of the United States from September to January with the peak in October–November. Based on plankton collections, mid-metamorphic larvae (stages G-H; mean s.l . 13.1 mm) enter Great Bay–Little Egg Harbor estuary in southern New Jersey as early as October with continued ingress through April. In the laboratory, mortality during metamorphosis ranged from 17 to 83% among treatment groups, and was significantly greater in flounder maintained at approximately 4°C relative to those maintained at ambient temperatures (daily average temperature 10.l°C). Laboratory-reared summer flounder averaged 24.5 days (range 20 to 32 days) to complete metamorphosis (from Stage F– to Stage I) at ambient spring temperatures (daily average temperature =16.6° C). The time to completion of metamorphosis in wild-caught flounder maintained in the laboratory was clearly temperature dependent. Both cold and ambient temperature treatments resulted in delayed metamorphosis such that, at ambient winter temperatures (daily average=6.6°C), partial metamorphosis (from Stage H – to Stage I) required as much as 92.9 days (range 67 to 99 days). There was no apparent effect of starvation on either mortality or time to completion of metamorphosis at cool water temperatures (< 10° C). It appears that prevailing temperature conditions influence the duration of metamorphosis in summer flounder, and that mortality during metamorphosis may play a significant role in the population dynamics of this species.     

Marine feeding of anadromous Salmo trutta during winter

Juvenile and adult anadromous trout Salmo trutta utilize the sea for feeding during the winter in the Skagerrak. This finding conflicts with the traditional view that anadromous trout overwinter in fresh water. Adults, just prior to spawning, were captured at sea in October to December, and spent fish were caught at sea from October to April, showing that the fish may leave the stream and move to sea just after spawning and spend the winter there. During mid‐winter (January to February), the feeding probability (chance of finding a fish with food in its stomach) increased markedly with increasing body length, with no similar effect during early and late winter (October to December and March to April). Among individuals with food in their stomach (72·5%), there was no evidence for variation in feeding intensity [stomach fullness = (mass of stomach content)(fish body mass)⁻¹] among early, mid‐, and late winter.     

Effects of photoperiod and temperature on the development of Bonagota cranaodes

Abstract.  The Brazilian apple leafroller, Bonagota cranaodes (Meyrick) (Lepidoptera: Tortricidae) is reared in the laboratory under a long-day (LD 14 : 10 h) and a short-day (LD 7 : 17 h) photoperiod at 22 °C, and under two different temperatures (10–13 °C and 21–22 °C). The development time from larval to adult eclosion do not differ between the two photoperiods, but did between the two temperature regimes. However, the larvae do not enter diapause, even under short day conditions and low temperatures. The number of adults obtained does not differ with temperature and light conditions. Field captures with pheromone traps show that Brazilian apple leafroller occurs in apple orchards throughout the year and the population densities are lower in winter. Accordingly, control measures should be taken during the off-season.     

Changes in gene expression of Scots pine buds during the winter and under experimentally altered light and temperature conditions

Vegetative buds of Scots pine ( Pinus sylvestris L.) were collected during the apparently dormant phase in January and February and at the beginning of the growth phase in May. Wintering Scots pine plants were placed in climate chambers in which either the daily photoperiod or the temperature simulated the situation in early spring, whereas the other conditions were characteristic of midwinter.
The amount of total ribosome populations and their in vitro translation capacities were independent of the height of the tree or place of collection, but both were dependent on the season; the amount of ribosomes per fresh weight of buds was lower in spring than in winter, whereas the translation capacity in spring exceeded that in winter. Poly(A)⁺ RNA was purified from the ribosomes and translated in vitro and the translation products were separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis. The polypeptide patterns proved that changes in gene expression can occur in plants growing outdoors even during the season of severe cold. In the climate chamber experiments, lengthening of the daily photoperiod increased the in vitro translation capacity of the buds within 7 days even at temperatures below 0°C, whereas a rise in temperature seemed to cause a more transient stress effect. Both treatments induced alterations in the pattern of in vitro polypeptide synthesis. It is suggested that while improvements in both light and temperature hastened the development of the buds under experimental growth conditions, the lengthening of the day may be the factor which induces a change in wintertime metabolism under natural conditions.     

Changes in growth performance and proximate composition in Japanese flounder during metamorphosis

Morphological changes are described in Japanese flounder Paralichthys olivaceus larvae and juveniles with emphasis on growth during the period of metamorphosis. Ontogenetic changes in condition factor and lipid, glycogen and protein levels were also analysed to determine the utilization of stored energy. Fish grew from 6·6 to 20·3 mm L _T(1·15 to 84·4 mg in mass, M ) during the period from 11 to 40 days after hatching (DAH) at 19·3° C. Per cent specific growth rate per day (% G day⁻¹) for wet mass was lowest during the metamorphic phase (21–30 DAH) compared to pre‐(11–20 DAH) and post‐metamorphic (31–40 DAH) phases. When L _T and M were expressed as     , the b value was highest during the pre‐metamorphic phase and lowest during the metamorphic phase. These findings indicate that the developmental changes that occur during metamorphosis of Japanese flounder are closely related to the growth pattern. Moisture, lipid and glycogen contents were also at the lowest level during metamorphosis compared to pre‐ and post‐metamorphosis, which suggest that Japanese flounder use their energy reserves to accomplish metamorphosis due to an apparent decline in feeding during this period.     

Role of environmental temperature and photoperiod in regulation of seasonal testicular activity in the frog, Rana perezi.

To analyze the role of environmental temperature and photoperiod in the regulation of the annual testicular cycle in Rana perezi, we performed experiments combining high (25 +/- 1 degrees C) or low (6 +/- 1 degrees C) temperature and different photoperiod regimens (18L:6D, 12L:12D, and 6L:18D (hours light:hours dark)) during three phases of the reproductive cycle: winter stage (December) and prebreeding (February) and postbreeding (May, June) periods. Low temperature and short photoperiod in winter induced the arrest of the maturation phase of spermatogenesis and the activation of primary spermatogonia proliferation and spermiohistogenesis. Rana perezi testis responded to long days stimulus in winter, even at low temperature, with induction of the maturation phase of the cycle. Exposure of male frogs to either high temperature or long photoperiod induced a decrease in testosterone levels in winter. During the prebreeding period, an increase in environmental temperature caused a reduction in testosterone, and a lengthening in photoperiod produced the opposite effect. Photoperiod had no effect on testosterone levels during the postbreeding period, but low temperature increased testosterone plasma levels. These results suggest that both temperature and photoperiod effects can vary seasonally, depending on the phase of the annual reproductive cycle in R. perezi.