ISSN 0012-4966, Doklady Biological Sciences, 2007, Vol. 413, pp. 121–124. © Pleiades Publishing, Ltd., 2007.Original Russian Text © V.V. Rozhnov, Sv.V. Naidenko, S.V. Naidenko, 2007, published in Doklady Akademii Nauk, 2007, Vol. 413, No. 1, pp. 138–141.

121

Three musteline species (Carnivora: Mustelidae)—the polecat

Mustela putorius

, European mink

M. lutre-ola

, and American mink

Neovison vison

—are differ-ently related to one another phylogenetically butinhabit similar periaquatic biotops with similar foodniches and feed on small rodents and amphibians. TheEuropean mink is a vulnerable species whose popula-tion density has been reducing in the past decades.Related species may play a role in this phenomenon,the mechanisms of which are intensely studied [1–3].Members of Mustelidae often display a pronouncedseasonal dynamics in physiological, behavioural, andpopulation processes. Analysis of social behavior ofsome species revealed seasonal changes in their socialstructures [4, 5], and the annual dynamics of the behav-ioural elements underlying this structure has beenquantitatively determined in the polecat [6].

Many physiological processes, especially reproduc-tive ones, are accompanied by hormonal changes thathave been studied in detail [7–9]. However, these hor-monal changes have never been studied as those corre-lated with behavioural features of many species.

The objective of this study was to determine sea-sonal changes in the levels of sex hormones (testoster-one, progesterone, and estradiol) and the glucocorticoidcortisol in both males and females of the above speciesof Mustelidae, as well as to evaluate the correlationbetween the hormonal changes and behavioural sea-sonal changes in these carnivores.

The experiments were conducted during an annuallife cycle of mustelids from June 2003 to August 2004at the Chernoglovka Research Station of the SevertsovInstitute of Ecology and Evolution, Russian Academyof Sciences. Blood samples were taken from animals

once a month at the same time of the day to exclude theeffect of the daily rhythms of the hormonal secretion.Blood plasma was separated by centrifugation at6000 rpm and kept at –20

°

C. The hormone concentra-tions were measured by enzyme immunoassay (EIA)using the commercial kits from Vector-Best (testoster-one and cortisol) and Chemi-Med (progesterone andestradiol).

Blood samples were obtained from 14 polecats(seven males and seven females), 9 American minks(four males and five females), and 5 European minks(five females). The data obtained were processes usingthe Statistica 6.0 software. The hormone concentrationswere compared monthly using the Mann–Whitney test.The testosterone concentration was compared in males;the estradiol and progesterone ones, in females,whereas the cortisol concentration was measured inboth males and females because sexual differences inthe amount of cortisol were not significant.

Our results showed that, in male polecats and Amer-ican minks, the level of testosterone grew substantiallyby the time of heat (by February and March for theAmerican mink and polecat, respectively) (Fig. 1). Sex-ual activity of male polecats was recorded as early as inDecember, when the testosterone concentrationincreased in the male blood plasma. The growing levelof testosterone reached the maximum in March, whenthis parameter exceeded that in any other month by afactor of 2 and when significant species differencesfrom the American mink were observed. In the polecatmales, an increased sexual activity and the high level oftestosterone were retained until August, and the ani-mals were obviously ready for mating at that time. Inthe male American minks, an increase in the level oftestosterone also coincided with the mating season(February), but this parameter was only 1.3–1.5 timeshigher at this time than in any other month. However,during the mating season, the absolute values of theaverage testosterone concentration were much lower inthe male American minks than in polecats (10.2 and

GENERAL BIOLOGY

Variation of the Level of Steroid Hormonesin the Blood Plasma of Three Mustelide Species

(Mammalia, Carnivora, Mustelidae) during the Annual Cycle

V. V. Rozhnov, Sv. V. Naidenko, and S. V. Naidenko

Presented by Academician D.S. Pavlov July, 24, 2006

Received November 9, 2006

DOI:

10.1134/S0012496607020081

Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Leninskii pr. 33, Moscow,117071 Russia

122

DOKLADY BIOLOGICAL SCIENCES

Vol. 413

2007

ROZHNOV et al.

39.0 ng/ml, respectively); the results of the Mann–Whitney test were the following:

n

1

= 2;

n

2

= 5;

U

= 0;

Z

= 2;

p

< 0.05. In the male American minks, the levelof testosterone grew as early as in December; after themating season time, this parameter decreased to thebasal level and reached the minimum by June (Fig. 1).From September to February, the testosterone concen-tration was higher in the American minks than in pole-cats, although significant differences were recordedonly in November. Thus, the level of testosterone inpolecat blood plasma differed significantly from thesame parameter in the American mink in two out ofeleven months.

The level of progesterone averaged about 0.8–4.1 ng/ml in females of the three mustelid species out-side the reproduction period (Fig. 2). During preg-nancy, this parameter increased strongly: 34 and

29 ng/ml in the American minks and polecats, respec-tively. After the birth of the offspring, the progesteroneconcentration reduced to the basal level by May in thefemale American minks and by June in the polecats.However, the progesterone concentration was still highfrom June to August in a few female polecats, whichconfirms sexual activity of the ovaries (pregnancy orovulation and false pregnancy in this period). In May–July, the level of progesterone was significantlyincreased (>6 ng/mg) in a greater percentage of mea-surements compared to other months (53.8%;

n

= 13and 2.6%;

n

= 38;

χ

2

= 133.1;

d.f.

= 1;

p

< 0.001). Peri-ods of male and female sexual activity coincided inpolecats (Figs. 1 and 2). In polecats and Americanminks, the levels of progesterone differed significantlyin March and November, whereas in polecats and Euro-pean minks, these parameters differed significantly in

10

0

January

Testosterone, ng/ml

±

SE

February

60

50

40

30

20

*

MarchApril

MayJune

JulyAugust

SeptemberOctober

NovemberDecember

1

2

10

0

January

Progestosterone, ng/ml

±

SE

February

50

40

35

30

20

*

MarchApril

MayJune

JulyAugust

SeptemberOctober

NovemberDecember

1

2

45

25

15

5

3

bb

b

*

*

Fig. 1.

The average level of testosterone (

M

±

SE

) in the blood plasma of the polecat and American mink. * Significant differencesbetween species (

p

< 0.05).

1

,

M. putorius, 2

,

N. vison.

Fig. 2.

The average level of progesterone (

M

±

SE

) in the blood plasma of female polecats, American minks, and European minks.Significant differences: * between American minks and polecats (

p

< 0.05) and

b

between American and European minks (

p

< 0.05).Here and in Figs. 3 and 4:

1

,

M. putorius

;

2

,

N. vison

;

3

,

M. lutreola.

DOKLADY BIOLOGICAL SCIENCES

Vol. 413

2007

VARIATION OF THE LEVEL OF STEROID HORMONES 123

March, April, and June. Two mink species had the samelevel of progesterone. In the female European minksthat had not mated, no increase in the blood plasmaprogesterone was recorded, which was correlated withthe absence of ovulation in during the year.

The average level of estradiol varied within a rangeof 0.05–0.4 ng/ml (outside the reproduction period)(Fig. 3). The basal level of these hormones was the

same in the three mustelid species. The estradiol con-centration increased only during estrus, which partlyexplains an increased level of estradiol in the femalepolecats in March and European minks in April, whenthe blood sampling coincided with the state of estrus insome females.

All the three species differed significantly from oneanother in the level of cortisol (Fig. 4). The highest

0

January

Estradiol, ng/g

±

SE

February

1.6

*

MarchApril

MayJune

JulyAugust

SeptemberOctober

NovemberDecember

1

2

0.2

3

b

1.4

0.4

0.6

0.8

1.0

1.2

Fig. 3.

The average level of estradiol (

M

±

SE

) in the blood plasma of female polecats, American minks, and European minks. Sig-nificant differences: * between American minks and polecats (

p

< 0.05) and

b

between American and European minks (

p

< 0.05).

0

January

Cortisol, ng/ml

±

SE

February

250

**

MarchApril

MayJune

JulyAugust

SeptemberOctober

NovemberDecember

1

2

3

b

50

100

200

150

**

a

** ** **

*

**

bb

**

Fig. 4.

The average level of cortisol (

M

±

SE

) in the blood of polecats, American minks, and European minks. Significant differ-ences: *, ** between American minks and polecats (

p

< 0.05 and

p

< 0.01, respectively) and between

b

American and

a

Europeanminks (

p

< 0.05).

124

DOKLADY BIOLOGICAL SCIENCES

Vol. 413

2007

ROZHNOV et al.

basal level of cortisol was in the American mink. In thepolecat and European mink, this parameter was muchlower. In the American mink, the level of cortisol dif-fered significantly from that in two other species inMarch, whereas in April–May and August–January, itdiffered from that in the polecat. In November–January,the average level of cortisol in the European mink wassignificantly higher than in the closely related polecatspecies.

Thus, the distinctions in the hormonal patterns ofthree mustelid species were the most pronounced forthe seasonal changes in the cortisol, progesterone, andtestosterone levels. Note that the mink species (belon-ing to different genera,

Neovison

and

Mustela

) differfrom each other to a greater extent than from the polecatin the level of the main steroid hormones. Changes inthe level of progesterone in females and testosterone inmales coincide with the periods of reproductive activityin the American mink and polecat.

Our data on the seasonal changes in the hormonalpatterns of the male polecats suggest a much more pro-longed activation of their sexual system than in themale American minks, which was correlated with sea-sonal changes in their reproductive activity studied bythe histological methods [10, 11]. The dynamics ofsocial behavior of male polecats and American minksproved to be related to the level of blood plasma test-osterone [4–6]. We showed previously that, in polecats,an increase in the level of testosterone in the periodfrom March to August was correlated with increasingaggressive interactions between males and with theproportion of avoidance among the total number ofsocial interactions [6]. In interrelations with females,the frequency of male-initiated aggressive contacts washigh in March and June–August.

In recent years, spontaneous ovulation was demon-strated to occur in a number of Carnivora, which werepreviously considered mammals with induced ovula-tion [12–14]. However, in female European minks iso-lated from males, no increase in the level of progester-one was found, which suggests that spontaneous ovula-tion is an extremely rare event in this species.

ACKNOWLEDGMENTS

This study was supported by the Program of BasicResearch of the Presidium of the Russian Academy ofSciences “Biodiversity and Gene Pool Dynamics” and

by the Program of the Division of Biological Sciencesof the Russian Academy of Sciences “BiologicalResources of Russia: Principles of Rational Use.”

REFERENCES

1. Rozhnov, V.V. and Petrin, A.A., in

Povedenie, kommuni-katsiya i ekologiya mlekopitayushchikh: Sb. nauch.rabot

(Behavior, Communication, and Ecology of Mam-mals: Collection of Research Works), Moscow: Inst.Probl. Ekol. Evol. Ross. Akad. Nauk, 1998, pp. 67–105.

2. Rozhnov, V.V. and Petrin, A.A.,

Dinamika populyatsiiokhotnich’ikh zhivotnykh Severnoi Evropy

(PopulationDynamics of Game Animals in Northern Europe) (Proc.II Int. Symposium, Sortavala, 2002), Petrozavodsk,2003.

3. Rozhnov, V.V. and Petrin, A.A.,

Povedenie i pove-dencheskaya ekologiya mlekopitayushchikh

(AnimalBehavior and Behavioral Ecology) (Proc. ScientificConference), Moscow: KMK, 2005.

4. Sokolov, V.E. and Rozhnov, V.V., in

Feromony i povede-nie

(Pheromones and Behavior), Moscow: Nauka, 1982,pp. 219–237.

5. Rozhnov, V.V.,

IV s’’ezd Vsesoyuz. teriolog. o-va: Tez.Dokl.

(Abstr. IV Congress of the All-Union HierologicalSociety), Moscow, 1986, pp. 159–160.

6. Rozhnov, V.V. and Naidenko, Sv.V.,

Povedenie, kommu-nikatsiya i ekologiya mlekopitayushchikh: Sb. nauch.rabot

(Behavior, Communication, and Ecology of Mam-mals: Collection of Research Works), Moscow: Inst.Probl. Ekol. Evol. Ross. Akad. Nauk, 1998, pp. 132–154.

7. Sundqvist, C., Lukola, A., and Valtonen, M.,

J. Reprod.Fertil.

, 1984, vol. 70, pp. 409–412.8. Young, K.M., Brown, J.L., and Goodrowe, K.L.,

ZooBiol.,

2001, vol. 20, pp. 517–536.9. Mustonen, A.-M., Saarel, S., Pyykonen, T., and Nie-

monen, P.,

Exp. Biol. Med.

, 2005, vol. 230, pp. 612–620.10. Danilov, P.I. and Tumanov, I.L.,

Kun’i severo-zapadaSSSR

(Mustelidae of theNorthwestern Soviet Union),Leningrad: Nauka, 1976.

11. Tumanov, I.L.,

Biologicheskie osobennosti khishchnykhmlekopitayushchikh Rossii

(Biological Characteristicsof Predatory Mammals of Russia), St. Petersburg:Nauka, 2003.

12. Concannon, P., Hodgson, B., and Lein, D., in

Reproduc-tion in Domestic Animals

, New York: Academic, 1991,4 edition, pp. 517–554.

13. Graham, L.H., Swanson, W.F., and Brown, J.L.,

Therio-genology

, 2000, vol. 54, pp. 117–131.14. Moreira, N., Monteiro-Filho, E.L.A., Moraes, W., et al.,

Zoo Biol.

, 2001, vol. 20, pp. 103–116.