Changes in Solea senegalensis sperm quality throughout the year

Some of the Senegalese sole (Solea senegalensis) broodstock reproductive constraints are related to sperm quality. Although they present two defined spawning season (spring and autumn), males gave semen during all the year thus an exhaustive annual sperm analysis is important to determine the seasonal changes in semen quality. Sampling was performed monthly during one year, analyzing different cellular parameters to better understand sperm quality limitations obstructing sole mass production. The percentage of progressive motile cells and their linear velocity showed a decrease from March (beginning of the first spawning season) to July (when the highest temperatures were observed), followed by a slight increase in August and October (second spawning season). DNA fragmentation values showed highest values between the two spawning seasons and decreased to the end of the year. The percentage of apoptotic cells was lowest in March (beginning of the first spawning season) and the highest in November. The percentage of cells resistant to seawater exposure presented two peaks related with both spawning seasons. There was a tendency for the semen to attain a quality peak between the beginning and the middle of the first spawning season (March-May), followed by a pronounced decrease, achieving the lowest values during the months with the highest temperature. Also, the different males present in the broodstocks reach their sperm quality peak at different times, which will result in an unequal contribution for the next generation.     

Sperm production, testicular size, serum gonadotropins and testosterone levels in Merino and Corriedale breeds

The relationships between testis size, hormone secretion and sperm production were studied during the spring (December) and autumn (May) in rams of two breeds with different breeding seasons and body weights (Corriedale and Australian Merino) maintained on native pastures and under natural photoperiods in Uruguay. Blood samples were collected at 20-min intervals during a 260-360-min period in 13 rams (four Corriedale, nine Australian Merino) during the late spring and autumn. Rams were weighed and testis size was estimated by orchimetry at each time period. Sperm production was estimated during a 2-week period, 2 months before blood collection and during each week following every blood collection. There was no relationship between testicular size and sperm production measured at the same time, nor between live weight and sperm production. In contrast, testicular volume during the late spring was correlated with sperm production in the autumn (r = 0.65; P = 0.02). The autumn serum LH was higher in Corriedale than in Merino rams. LH pulsatility was unaffected by season, but LH pulse frequency tended to be higher in Corriedale than in Merino rams, particularly in the late spring (2.37 versus 1.56 pulses/6 h; P = 0.08). Serum testosterone concentration was similar in both breeds and seasons. FSH levels were higher in the late spring than in the autumn in both breeds (Corriedale: 2.83 +/- 0.48 versus 2.17 +/- 0.24 ng x mL(-1); Merino: 2.23 +/- 0.24 versus 1.88 +/- 0.17 ng x mL(-1)). FSH and testosterone concentrations during the late spring were positively correlated with autumn sperm production (P = 0.07 and P = 0.03, respectively). In conclusion, the present experiment suggests that LH secretion is not a good parameter for the prediction of sperm production. In contrast, in our conditions (breeds and native pastures) testicular size and testosterone or FSH concentrations from the late spring may be used to predict sperm production in the autumn.     

Seasonal effects on sexual maturation of male bank voles (Clethrionomys glareolus)

The weights of the testes and accessory glands, and the degree of morphological and functional development of the seminiferous tubules, were used as indicators of sexual maturation in male bank voles. Males reared under constant laboratory conditions showed a significant relationship between the seasons and sexual maturation. Young males reached maturity most rapidly in the reproduction season (mid-April to mid-October), while adult males matured earlier, in the spring season (mid-January to mid-April). The influence of season on animals reared in outdoor cages was much more pronounced. One of the important factors was the photoperiod: animals reared from 3 to 12 weeks of age in a short photoperiod (8L:16D) matured less rapidly than did those reared in 16L:8D.     

Seasonal changes of semen quality and freezability in Franches-Montagnes stallions

The objective of this study was to investigate seasonal changes of semen quality parameters in Franches-Montagnes stallions and to compare the freezability of ejaculates collected in autumn and winter. Experiments were performed using 15 stallions from the National Stud Farm in Avenches (Switzerland). Ejaculates were collected and evaluated every month during 1 year as well as cryopreserved in autumn and winter (September to February). In fresh semen the gel-free volume, concentration, motility and morphology (normal sperm, major defects, vacuoles and acrosome defects) were evaluated and in frozen-thawed semen the motility as well as the viability (SYBR-14/PI) were performed. To analyse seasonal differences four periods of 3 months each were defined as autumn (September, October, November), winter (December, January, February), spring (March, April, May) and summer (June, July, August). During the 1-year experiment all fresh semen quality parameters demonstrated a clear seasonal and individual pattern. The gel-free volume was significantly (P<0.05) higher in spring and summer compared to autumn and winter while sperm concentration was significantly (P<0.05) lower in spring than at any other time of the year. Total sperm number was significantly (P<0.05) higher and sperm motility significantly (P<0.05) lower in summer than in other seasons. Regarding sperm morphology, normal sperm was significantly (P<0.05) higher in autumn than in winter and summer and major defects were lowest (P<0.05) in autumn. In frozen-thawed semen motility was significantly (P<0.05) improved in the ejaculates collected in autumn compared to winter, while viability showed no obvious differences. Our results clearly demonstrate that individual and seasonal differences occurred in semen quality of Franches-Montagnes stallions. Ejaculates collected in autumn (September, October, November) demonstrated good quality, especially regarding sperm morphology, and were more suitable for cryopreservation because of better motility in frozen-thawed semen collected during autumn than in winter.     

Is lack of mating competitiveness in spring linked to mating asynchrony between wild and mass‐reared codling moths from an operational sterile insect programme?

Mating competitiveness and pheromone trap catches of mass‐reared, male codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), from the Osoyoos, British Columbia, Canada, mass‐rearing facility operated by the Okanagan‐Kootenay Sterile Insect Release Board, were compared to wild males using mark–release–recapture field experiments in spring, summer, and autumn at Summerland, British Columbia. In spring, significantly more wild diapause males mated with tethered, wild females than did non‐irradiated (0 Gy) or irradiated (100 or 250 Gy) non‐diapause, mass‐reared males. A lower dose of radiation did not improve mating competitiveness, nor catches of mass‐reared males released in spring. Median mating time for wild males was approximately 45 min earlier than mass‐reared males with most wild males (70.5%) mating before sunset and mass‐reared males mating at or shortly after sunset in spring. Superior mating competitiveness of wild males in spring was mirrored by greater recapture rates in pheromone‐baited traps. In summer, mating competitiveness of mass‐reared moths improved relative to wild males and there was a significant inverse relationship between radiation dose (0, 100, and 250 Gy) and competitiveness of mass‐reared males. In autumn, untreated, wild males were significantly more responsive to pheromone traps than non‐diapausing mass‐reared males receiving 250 Gy of radiation. Mass‐reared males, subjected to diapause‐inducing conditions as larvae and emerged from diapause before this irradiation treatment, were recaptured significantly more often than similarly irradiated, non‐diapause, mass‐reared males, but not more than untreated, diapause wild males. We hypothesize that differences between wild and mass‐reared males in daily timing or speed of responses to natural or synthetic pheromone sources under montane weather patterns typical of spring in British Columbia may partially explain poor activity of sterile males, and low sterile : wild overflooding ratios during spring when measured using pheromone traps by the sterile insect release programme in British Columbia.     

Seasonal changes in semen quality and freezability in the Warmblood stallion

The objective of this study was to investigate seasonal changes in stallion semen quality and to determine the best time for semen cryopreservation. Experiments were performed using 10 Warmblood stallions from the National Stud Farm in Avenches (Switzerland). Ejaculates were collected and frozen every other week during 1 year from January to December 1999. Volume, concentration, and motility, and the number of morphologically normal sperm and sperm with major defects (abnormal heads, acrosome defects, nuclear vacuoles, proximal droplets, abnormal midpieces) were evaluated. For all frozen-thawed semen samples motility as well as viability (SYBR-14/PI) was tested, and the hypoosmotic swelling test (HOS) was performed. To analyze seasonal differences 4 periods of 3 months each were defined: autumn (September, October, November), winter (December, January, February), spring (March, April, May) and summer (June, July, August). During the 1 year experiment all semen quality parameters showed a clear seasonal pattern. The volume, total sperm count and motility in fresh semen were significantly higher (P<0.05) in summer than in winter, while sperm concentration was significantly lower in summer compared to the other seasons. Regarding morphology, normal sperm was significantly lower (P<0.05) in summer than at any other time of the year and higher values (P<0.05) were found for major defects in summer than in spring and autumn. In frozen-thawed semen motility was significantly (P<0.05) improved in autumn when compared to spring and summer. Viability was lowest in summer and differed significantly (P<0.05) from other seasons. The HOS test revealed significantly more (P<0.05) membrane damaged spermatozoa in winter than in spring, summer and autumn. Our results demonstrate that in our climatic conditions clear seasonal differences occur in semen quality of fresh and frozen-thawed semen and that cryopreservation of stallion semen should preferably be performed in autumn.     

Chilled storage of semen from Atlantic halibut, Hippoglossus hippoglossus L. II: effect of spermiation advancement, catheterization of semen, and production-scale application

A method for in vitro storage of Atlantic halibut Hippoglossus hippoglossus L. semen can facilitate seed production. The study aimed at determining the effect of male spermiation advancement on viability of chilled stored spermatozoa. The use of catheterization of semen from the sperm duct was examined. Also, large volumes of semen were stored under sub-optimal production-like conditions in order to determine the suitability of the method into practical use. Semen was collected from two broodstocks: natural photoperiod males, being at the first phase of the reproductive season and 3-month advanced photoperiod males, being at the end of the reproductive season. Semen samples were diluted 1:5 (v/v) with modified Hanks' Balanced Salt Solution supplemented with antibiotics, and stored in Ziploc bags filled with air. Sperm motility parameters, assessed by computer-assisted sperm analysis (CASA), were assessed weekly. Experimental and production-scale fertilization trials were performed. Sperm samples from natural photoperiod males showed significantly longer viability under in vitro storage conditions than sperm from advanced photoperiod males. In the natural photoperiod group, the decrease in spermatozoa motility, curvilinear velocity and straight-line velocity occurred on day 50, 14, and 28 of storage, respectively. Spermatozoa from one of five males were still motile on day 80 of storage, and fertilization rates and embryo survival rates obtained using semen stored for 70 days did not differ from control values and they were significantly higher than values obtained with the use of fresh semen of the same male, but being at the end of reproductive season. Catheterization of semen showed no advantage to stripping the semen without a catheter, even for samples stored undiluted for 1 day of collection, before dilution. Under sub-optimal conditions, spermatozoa stored in large volumes (10-100mL of diluted semen) without any special treatments except for weekly swirling, remained viable for more than 1 month. Production-scale fertilizations with samples stored for 5-21 days resulted in high survivals of embryos and hatchlings. Because of its simplicity and efficiency, the method shows a high potential for use in commercial Atlantic halibut farming. It has already been applied to a halibut breeding programme for the next reproductive season at our research station.     

Season of ejaculate collection influences the freezability of boar spermatozoa

The aim of this retrospective study was to evaluate whether the season of ejaculate collection influences the freezability of porcine sperm. A total of 434 ejaculates were collected from boars of six different breeds over three years (2008–2011) and throughout the four seasons of the year identified in the northern hemisphere (winter, spring, summer and autumn). The ejaculates were cryopreserved using a standard 0.5 mL straw freezing protocol. Sperm quality was assessed before (fresh semen samples kept 24 h at 17 °C) and after freezing and thawing (at 30 and 150 min post-thawing in semen samples kept in a water bath at 37 °C), according to the percentages of total motility, as assessed by the CASA system, and viability, as assessed by flow cytometry after staining with SYBR-14, PI and PE-PNA. The data, in percentages, on sperm motility and viability after freezing and thawing were obtained at each evaluation time (recovered) and were normalized to the values before freezing (normalized). The season of ejaculate collection influenced (P < 0.01) sperm quality before freezing and after thawing (recovered and normalized), irrespective of the breed of boar. Sperm quality was lower in summer, both in terms of motility and viability, and in autumn, in terms of motility, than in winter and spring. Seasonality in the normalized data indicates that the season of ejaculate collection influences sperm freezability, regardless of the season’s influence on sperm quality before freezing. Consequently, the spermatozoa from ejaculates collected during summer and, to a lesser extent, also in autumn, are more sensitive to cryopreservation than those from ejaculates collected during winter and spring.     

Seasonal variation in reproductive physiological status in the Iberian ibex (Capra pyrenaica) and its relationship with sperm freezability

The present work examines the relationship between seasonal changes in testicular function, accessory gland size, and horn growth in Iberian ibexes, as well as the relationship between these changes and the resistance of ibex spermatozoa to freezing-thawing. The size of the bulbourethral glands and seminal vesicles showed pronounced monthly variation (P < 0.001), which was correlated positively with the plasma testosterone concentration (P < 0.001) and scrotal circumference (P < 0.001). The size of the accessory sex glands peaked during the autumn. Overall, semen quality was markedly improved during autumn and winter. When horn growth was at a minimum during autumn and winter, semen quality and accessory gland size were all increased compared to in spring and summer. However, increased plasma testosterone levels in the autumn were strongly associated with reduced sperm freezability; thus, the cryosurvival of spermatozoa collected during the autumn was poorer than at other times of the year. In winter, however, when the plasma testosterone concentration fell to baseline, the negative effects of cryopreservation on the percentage of motile spermatozoa and on the integrity of the plasma membrane of frozen-thawed sperm cells were significantly less intense (P < 0.05). These findings show a clear relationship between the functional and morphological status of the different parts of the reproductive tract that optimises reproductive function during the breeding season in the ibex male. They also show that winter is the most suitable season for the collection and cryopreservation of ibex spermatozoa.     

Seasonal variation in reproductive physiological status in the Iberian ibex (Capra pyrenaica) and its relationship with sperm freezability

The present work examines the relationship between seasonal changes in testicular function, accessory gland size, and horn growth in Iberian ibexes, as well as the relationship between these changes and the resistance of ibex spermatozoa to freezing-thawing. The size of the bulbourethral glands and seminal vesicles showed pronounced monthly variation (P < 0.001), which was correlated positively with the plasma testosterone concentration (P < 0.001) and scrotal circumference (P < 0.001). The size of the accessory sex glands peaked during the autumn. Overall, semen quality was markedly improved during autumn and winter. When horn growth was at a minimum during autumn and winter, semen quality and accessory gland size were all increased compared to in spring and summer. However, increased plasma testosterone levels in the autumn were strongly associated with reduced sperm freezability; thus, the cryosurvival of spermatozoa collected during the autumn was poorer than at other times of the year. In winter, however, when the plasma testosterone concentration fell to baseline, the negative effects of cryopreservation on the percentage of motile spermatozoa and on the integrity of the plasma membrane of frozen-thawed sperm cells were significantly less intense (P < 0.05). These findings show a clear relationship between the functional and morphological status of the different parts of the reproductive tract that optimises reproductive function during the breeding season in the ibex male. They also show that winter is the most suitable season for the collection and cryopreservation of ibex spermatozoa.     

Changes in sperm parameters of sex-reversed female rainbow trout during spawning season in relation to sperm parameters of normal males

The production of all-female populations has important economic benefits in commercial rainbow trout aquaculture. The procedure commonly implemented to produce all-female stocks centers on the sex reversal of rainbow trout females via the administration of androgens in the early developmental stages, followed by the egg fertilization of normal females with semen from sex-reversed females (srf). However, there is no information regarding the quality of semen from srf rainbow trout throughout the spawning season. This information is critical because the quality of srf semen is highly variable. The aim of the study was to determine the changes in the semen parameters of srf rainbow trout throughout the duration of the spawning season. Sperm concentration, sperm motility parameters, and the biochemical parameters of seminal plasma (protein concentration, antitrypsin activity, osmolality, and lactate dehydrogenase activity) from srf were monitored during the spawning season and compared with normal male rainbow trout. The observed values of sperm, protein concentration, antitrypsin activity, osmolality, and lactate dehydrogenase activity of seminal plasma were all higher in comparison with normal males. Semen from srf was therefore characterized by a lower sperm motility during each period of the spawning season, in comparison with normal males, approximately 1.8, 1.5, and 1.7 times, respectively for the beginning, middle, and end of the spawning season. The percentage of sperm motility from srf and normal males were affected by the spawning season in the same way, as the highest values in the middle of the spawning season demonstrate (60% and 91% for srf and normal males, respectively). Spermatozoa of srf are characterized by a lower speed and a more curvilinear trajectory of movement as compared with that of normal males. The patterns of changes during the spawning season in sperm concentration, sperm motility parameters, as well as osmolality, and lactate dehydrogenase activity of the seminal plasma of srf were different in comparison with normal males. Our results could be important for fish breeders in regard to the spawning control of srf rainbow trout, as well as for the development of short- and long-term sperm storage procedures.     

Larval food composition affects courtship song and sperm expenditure in a lekking moth

1. Variation in larval food composition can have far‐reaching effects on the adult phenotype of insects. To maximise reproductive output, it is therefore beneficial if insects are able to plastically adapt to nutritional cues in their larval diet. 2. The expression of sexual traits implicated in pre‐ and postcopulatory sexual selection of the lesser wax moth, Achroia grisella Fabricius, across different rearing environments of varying diet composition was investigated. 3. Moths reared on diet with relatively low amounts of carbohydrate, but more protein and fats, had lower survival rates, decreased body mass, and longer development times. Males reared on this diet produced songs with higher pulse pair rates (which are attractive to females) and transferred more sperm per copulation than males reared on the alternative diets. 4. There was no evidence for a trade‐off between pre‐ and postcopulatory traits. Interestingly, individuals with both higher pulse pair rates and more transferred sperm came from the treatment group with higher mortality rates and generally poorer development. The present results suggest that both of these sexual characteristics are developmentally plastic, but that only moths reared on the protein‐rich diet were able to benefit from this plasticity.     

Characteristics and seasonal variation in the semen of Markhoz bucks in western Iran

The aims of the present study were to evaluate if seasonality in semen characteristics and plasma testosterone concentrations exist in Markhoz male goats. Ten Markhoz (Angora) bucks were housed and fed according to standard recognized practices. During the observation period, semen was collected monthly with the aid of an electro-ejaculator and examined microscopically immediately after collection. Physical parameters of semen and the semen index were recorded. Blood samples were also taken monthly throughout the observation period and the plasma testosterone concentration monitored. Bucks demonstrated a higher semen quality (P < 0.05) in autumn and summer (semen index of 965 × 10⁶ and 752 × 10⁶ ml⁻¹, respectively), compared to spring and winter (semen index of 606 × 10⁶ and 512 × 10⁶, respectively). This coincided with a higher (P < 0.05) plasma testosterone concentration in autumn and summer (8.1 and 10.1 ng ml⁻¹, respectively), compared to that obtained in spring (3.0 ng ml⁻¹) and winter (2.5 ng ml⁻¹). During autumn and summer, the ejaculate volume (average of 1.2 and 1.0 ml), sperm output (1159 × 10⁶ and 1005 × 10⁶ sperm ml⁻¹), sperm mass motility (4.2 and 4.3), sperm progressive motility (83.9 and 82.0%) and percentage live sperm (90.7 and 88.2%, respectively) of the bucks were higher (P < 0.05) than in the spring (0.6 ml, 880 × 10⁶ sperm ml⁻¹, 3.3, 71.5% and 80.2%) and winter (0.7 ml, 863 × 10⁶ sperm ml⁻¹, 4.0, 71.5% and 84.9%, respectively). During autumn and summer, the percentage of sperm abnormalities (5.0 and 9.2%) was significantly lower than that in spring (12.9%) and winter (11.2%). The semen pH was slightly alkaline being significantly (P < 0.05) lower in the autumn (7.1) than in spring (7.3). Data showed season of the year to influence all semen parameters evaluated—indicating that optimal buck performance may be obtained in late summer and autumn. It can thus be said that Markhoz bucks have distinct seasonal spermatogenic activity, with poorer semen characteristics being recorded during winter and spring. This may be a critical obstacle when implementing an intensive breeding system of three kidding seasons in 2 years, with natural mating being implemented.     

Life histories of Atlantic salmon altered by winter temperature and summer rearing in fresh- or sea-water

Increased growth during winter increased the incidence of age 1+ Salmo salar smolts in spring. High condition factor in spring and good growth in summer was associated with a high incidence of sexually mature males in autumn. In two experiments, groups (n=160–237 per group) of individually identified parr, either ungraded (lower and upper modal groups: LMG, UMG) or size-graded (LMG only), were reared at either 10, 6 or 3 °C overwinter (Nov to May). At 10 °C, up to 51% of parr originally in the LMG became smolts in spring at age 1+. In contrast, at either 6 or 3 °C (control), < 6% of LMG parr became smolts. The probability of being recruited into the UMG overwinter was positively related to initial body size, and was increased by size-grading. Smolt recruitment was two-fold higher among females compared to males; a proportion of males by age 0+ had already opted to mature at age 1+ rather than smolt at age 1+. In contrast, smolting at age 1+ was not inhibited in males previously mature at age 0+. During summer (May to Nov), all experimental groups were reared at ambient temperature, each subdivided between fresh water (max 21 °C) or seawater (max 15 °C). Good growth in seawater of winter recruits into the UMG confirmed they had completed smolting. Mortality in seawater among parr was 41–83%, and among smolts was 10–22%. Specific growth rate during summer was inversely related to winter rearing temperature. The incidence of sexual maturity in autumn at age 1+ among male parr was positively related to winter rearing temperature, fork length and condition factor in May, but there was large variation among individuals with respect to body size and maturity. Summer rearing in seawater reduced growth and the incidence of maturation. Parr and post-smolt maturity was 84–99% and 100% in fresh water respectively, 21–58% and 0% in seawater.     

Female choice and the benefits of mate guarding by male mallards

Pair formation and breeding in many species of waterfowl are separated both temporally and spatially. Most studies of female choice in this group have focused on male characteristics at the time of pairing, with less attention given to how mate choice affects breeding season outcomes. In this study I compared pairing success, male plasma testosterone level and mate-guarding ability of male mallards, Anas platyrhynchos, in two experiments. In the first experiment females and males were group housed with equal sex ratios, thus allowing all of these males to pair. At the same time, an equal number of males was housed in groups without access to females and remained unpaired. In this experiment testosterone levels of paired and unpaired males during autumn (baseline) and spring (breeding) did not differ, indicating that the process of pair formation and breeding does not cause elevated spring testosterone levels in males. However, testosterone did temporarily decrease in paired males during the winter (pair formation) season. In the second experiment groups were male biased, allowing only half of the males to pair. Here paired males had significantly higher testosterone levels than unpaired males during the breeding season, but not during the preceding autumn. Together the results of these experiments indicate that successful pair formation predicts but does not alter male testosterone level during the breeding season. I also found that females paired to males with high levels of testosterone were missing fewer feathers due to forced copulation attempts by nonmates, suggesting that females may choose males based on their mate-guarding abilities. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Developmental temperature affects the expression of ejaculatory traits and the outcome of sperm competition in Callosobruchus maculatus

The outcome of post‐copulatory sexual selection is determined by a complex set of interactions between the primary reproductive traits of two or more males and their interactions with the reproductive traits of the female. Recently, a number of studies have shown the primary reproductive traits of both males and females express phenotypic plasticity in response to the thermal environment experienced during ontogeny. However, how plasticity in these traits affects the dynamics of sperm competition remains largely unknown. Here, we demonstrate plasticity in testes size, sperm size and sperm number in response to developmental temperature in the bruchid beetle Callosobruchus maculatus. Males reared at the highest temperature eclosed at the smallest body size and had the smallest absolute and relative testes size. Males reared at both the high‐ and low‐temperature extremes produced both fewer and smaller sperm than males reared at intermediate temperatures. In the absence of sperm competition, developmental temperature had no effect on male fertility. However, under conditions of sperm competition, males reared at either temperature extreme were less competitive in terms of sperm offence (P₂), whereas those reared at the lowest temperature were less competitive in terms of sperm defence (P₁). This suggests the developmental pathways that regulate the phenotypic expression of these ejaculatory traits are subject to both natural and sexual selection: natural selection in the pre‐ejaculatory environment and sexual selection in the post‐ejaculatory environment. In nature, thermal heterogeneity during development is commonplace. Therefore, we suggest the interplay between ecology and development represents an important, yet hitherto underestimated component of male fitness via post‐copulatory sexual selection.     

Sibling rivalry: Males with more brothers develop larger testes

When females mate with multiple partners in a reproductive cycle, the relative number of competing sperm from rival males is often the most critical factor in determining paternity. Gamete production is directly related to testis size in most species, and is associated with both mating behavior and perceived risk of competition. Deer mice, Peromyscus maniculatus, are naturally promiscuous and males invest significantly more in sperm production than males of P. polionotus, their monogamous sister‐species. Here, we show that the larger testes in P. maniculatus are retained after decades of enforced monogamy in captivity. While these results suggest that differences in sperm production between species with divergent evolutionary histories can be maintained in captivity, we also show that the early rearing environment of males can strongly influence their testis size as adults. Using a second‐generation hybrid population to increase variation within the population, we show that males reared in litters with more brothers develop larger testes as adults. Importantly, this difference in testis size is also associated with increased fertility. Together, our findings suggest that sperm production may be both broadly shaped by natural selection over evolutionary timescales and also finely tuned during early development.     

The annual reproductive cycle of the Smooth newt (Triturus vulgaris) in England

Newts were collected throughout the year from both breeding ponds and terrestrial sites and were weighed, measured and dissected; in males, the testes were examined histologically. Smooth newts show post-nuptial gametogenesis such that, during late summer and autumn they are producing mature gametes for the following year's breeding season. In males, the testes are at their smallest size during the spring, when they consist mostly of immature sperm cysts and evacuated tissue, mature sperm having been evacuated into the vasa deferentia during the newts' migration to water. Evacuated testicular tissue is glandular in function and there is evidence that secretions from this tissue control the development of secondary sexual characters: the dorsal crest, fringes of skin on the toes and the dorsal cloacal gland. In both sexes, fat body and liver weights are lowest in the spring and increase in the autumn. In females, oocytes vary in size, depending on the amount of yolk they contain. Only the larger oocytes are laid in a current breeding season, the smaller ones being retained and yolked in late summer and autumn. In both sexes, measures of fecundity (testis size in males, oocyte number in females) are strongly correlated with body size. The finding that male newts have a finite supply of sperm during the breeding season leads to an interpretation of various aspects of male courtship behaviour. These are adaptations for conserving sperm and allocating it to courtship encounters in a way likely to promote male reproductive success.     

Home range size and activity of the wood lemming, Myopus schisticolor

We present the results from a radiotelemetric study on space use and activity in a natural population of the wood lemming Myopus schisticolor. Male home ranges were larger than females, and the ratio female home range to male home range was smaller than expected compared to other small rodents. Males moved distances 4-12 times longer than females. We argue that this difference in mobility gives a higher probability of capturing males than females in snap trap studies. If there is a sex biased trappability, this might explain the increasing female biased sex ratio during the snow free season (1:1 in spring, 3:1 [female:male| in autumn), as a higher mortality of males during the reproductive season.     

Postpubertal sexual development in merino rams after differential feeding through puberty

Spring-born Merino ram lambs were reared on 130%, 165% or 200% of recommended maintenance energy requirements from 7 to 12 mo of age and were then placed on a common plane of nutrition from 12 to 25 mo of age. During the latter 13 mo, the 24 rams were studied for changes in live-weight and testicle characteristics. Semen characteristics and sexual activity were observed from 12 to 19 mo of age. At the beginning of the study, groups coming from low (L), medium (M), and high (H) nutrition had liveweights of 38.9, 46.8, and 53.6 kg (P < 0.05) and scrotal circumferences of 24.6, 28.9, and 32.1 cm (P < 0.05), respectively. When the rams were given common feed conditions, the differences between groups in both liveweight and scrotal circumference quickly decreased and were not significant by the sixth month. No significant differences existed between groups in ejaculate characteristics during semen collection, except in sperm density which, at the end of semen collection, was significantly (P < 0.05) higher in Group M (3.98 x 10(9)/ml) than in Group L (2.55 x 10(9)/ml). However, in analyses of pooled data, there were significant differences between months of collection in sperm density, total number of sperm per ejaculate, and percentages of live and abnormal sperm. The data indicate that differential nutrition during the first year of life will affect some reproductive characters contemporaneously, but with restored feeding, reproductive differences are resolved more quickly than those in liveweight and the changes proceed despite countervailing photoperiodic influences.