Social environment modulates photoperiodic immune and reproductive responses in adult male white-footed mice<i>(Peromyscus leucopus)</i>

General and Comparative Endocrinology

Greiwe

et al. 2006

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At temperate latitudes, mammals and birds use changes in day length to time their reproductive activities to coincide with seasonal fluctuations in the environment. Close to the equator, however, conditions permissive of breeding do not track changes in day length as well, so other cues may be more important than photoperiod. In a variety of vertebrates, social interactions regulate breeding condition. We hypothesized that individuals of different species of Peromyscus mice found closer to the equator would respond more strongly to housing with an opposite sex conspecific than they would to photoperiod. To test this hypothesis, we compared the effects of long and short day lengths versus 8 days of pair housing with a female on reproductive tissue weights and testosterone (T) concentrations in five species of Peromyscus (P. aztecus, P. eremicus, P. maniculatus, P. melanophrys, and P. polionotus). After 13 weeks of short days (8L:16D), P. maniculatus, P. melanophrys, and P. polionotus significantly reduced relative testes mass compared to long day (16L: 8D) housed animals. Social housing, however, had no effect on tissue weights in any species. However, male P. polionotus paired with females for 8 days increased T concentrations compared to single-housed males, whereas paired P. maniculatus reduced T. These data suggest that mechanisms of photoperiodic and social regulation of reproductive function are mediated by different physiological mechanisms among closely-related species and that both phylogeny and environmental factors contribute to patterns of reproductive plasticity.

Section: Discussionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Social and photoperiod effects on reproduction in five species of Peromyscus

Trainor

General and Comparative Endocrinology

Greiwe

et al. 2006

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“…Some rodents also allocate to immune defence differently depending on latitude. Aztec mice (Peromyscus aztecus), which reside in southern Mexico, show no immunological responsiveness to the changes in day length , whereas more northerly distributed species (northern USA) show enhanced responses in short days coupled with reduced responses in long days when breeding typically occurs (Pyter et al 2005a). Recent work in meadow voles (Microtus pennsylvanicus) indicates that the effects of latitude on immune activity may be complicated in some cases.…”

Section: K1mentioning

confidence: 99%

Seasonal changes in vertebrate immune activity: mediation by physiological trade-offs

Weil

Nelson

2007

Phil. Trans. R. Soc. B

470

496

Animals living in temporally dynamic environments experience variation in resource availability, climate and threat of infection over the course of the year. Thus, to survive and reproduce successfully, these organisms must allocate resources among competing physiological systems in such a way as to maximize fitness in changing environments. Here, we review evidence supporting the hypothesis that physiological trade-offs, particularly those between the reproductive and immune systems, mediate part of the seasonal changes detected in the immune defences of many vertebrates. Abundant recent work has detected significant energetic and nutritional costs of immune defence. Sometimes these physiological costs are sufficiently large to affect fitness (e.g. reproductive output, growth or survival), indicating that selection for appropriate allocation strategies probably occurred in the past. Because hormones often orchestrate allocations among physiological systems, the endocrine mediators of seasonal changes in immune activity are discussed. Many hormones, including melatonin, glucocorticoids and androgens have extensive and consistent effects on the immune system, and they change in systematic fashions over the year. Finally, a modified framework within which to conduct future studies in ecological immunology is proposed, viz. a heightened appreciation of the complex but intelligible nature of the vertebrate immune system. Although other factors besides tradeoffs undoubtedly influence seasonal variation in immune defence in animals, a growing literature supports a role for physiological trade-offs and the fitness consequences they sometimes produce.

“…All mice were sensitized to 2, 4-dinitro-1-fluorobenzene (DNFB; Sigma-Aldrich, St. Louis, MO, USA) by applying 50μL of DNFB [0.5% (w/v) in 4:1 acetone/olive oil vehicle] to a shaved area on the rump for two consecutive days while each mouse was under anesthesia (isoflurane in O 2 enriched-air) (Pyter et al 2005b;Martin et al 2006b). One week later, mice were again anesthetized, and thicknesses of pinnae were measured using a constant-loading micrometer (Mitituyo, Tokyo).…”

Section: Delayed-type Hypersensitivity (Dth)mentioning

confidence: 99%

“…We assessed effects of 6-MBOA on reproductive parameters and DTH in long-day breeding whitefooted mice. This species was chosen because individuals i) exhibit seasonal changes in immune activity and reproductive capacity (Johnston et al 1980b;Pyter et al 2005b), ii) some of these changes are mediated by melatonin (Johnston et al 1980a;Glass et al 1988), and iii) individuals consume a variety of foods in the wild, including plants (King 1968). Other species known to be sensitive reproductively to 6-MBOA have not been as well characterized.…”

Section: Introductionmentioning

confidence: 99%

6-MBOA affects testis size, but not delayed-type hypersensitivity, in white-footed mice (Peromyscus leucopus)

Comparative Biochemistry and Physiology Part A: Molecular &

Johnson

Hutch

et al. 2008

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Many rodents use day length to time reproduction to occur when resources are abundant, but some species also use supplementary environmental cues. One supplementary cue is the plant-derived compound, 6-methoxy-2-benzoxazolinone (6-MBOA). Most rodents grow their gonads in response to 6-MBOA in their diets, but it is presently unknown whether they also use 6-MBOA to adjust other aspects of physiology, specifically their immune systems. 6-MBOA is structurally similar to melatonin, and seasonal changes in rodent immune activities are often mediated by melatonin. We therefore predicted that white-footed mice (Peromyscus leucopus), which breed seasonally and are reproductively sensitive to melatonin, would adjust their immune systems when fed 6-MBOA. 6-MBOA treated mice in long day lengths regressed their testes to a greater extent than mice fed a standard diet, or mice kept in short day lengths and fed 6-MBOA or a standard diet. One type of immune activity (delayed-type hypersensitivity) was not affected by 6-MBOA, however, although responses were greater in short versus long day mice. In sum, P. leucopus responded reproductively to 6-MBOA, although differently than other species; immune activity was unaffected. Other aspects of the immune system, especially in herbivorous rodents, may be affected by 6-MBOA and thus warrant further study.