Seasonal breeder
Encyclopedia
Seasonal breeders are animal
species
that successfully mate only during certain times of the year. These times of year allow for the births at a time optimal for the survival of the young in terms of factors such as temperature, food and water. Related sexual interest and behaviors are expressed and accepted only during this period. Female seasonal breeders will have one or more estrus cycles only when she is "in season" or fertile and receptive to mating. At other times of the year, they will be anestrus. Similarly, male seasonal breeders may exhibit changes in testosterone
levels, testes weight and fertility depending on the time of year.
Seasonal breeders are distinct from opportunistic breeders
, which mate whenever the conditions of their environment become favorable, and continuous breeders like humans that mate year-round.
is considered to be the central control for reproduction. Hence, factors that determine when a seasonal breeder will be ready for mating affect this tissue. This is achieved specifically through changes in the production of the hormone GnRH. GnRH in turn transits to the pituitary where it promotes the secretion into the bloodstream of the gonadotropin
LH
, a pituitary hormone
critical for reproductive function and behavior. Changes in gonadotropin secretion initiate the end of anestrus in females.
secretion by the pineal gland
that ultimately alter GnRH release by the hypothalamus.
Hence, seasonal breeders can be divided into groups based on when they are fertile. "Long day" breeders cycle when days get longer (spring) and are anestrus in fall and winter. "Short day" breeders cycle when the length of daylight shortens (fall) and are anestrus in spring and summer. Domestication has allowed cattle and swine to be liberated from breeding seasonality.
Day length variations with latitude can also impact breeding. For instance, sheep and goats in tropical climes may breed throughout the year while those in more polar arctic areas may have a shortened season.
Females are generally more sensitive to changes in day length. For instance, unlike mares, stallions remain fertile year-round, suffering only some declines in sexual behavior and sperm production
out of season.
Further environmental factors can include nutrition, chemosensory and hormonal cues. Weight and age are other factors.
. Here is partially listed those that are mammals.
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
that successfully mate only during certain times of the year. These times of year allow for the births at a time optimal for the survival of the young in terms of factors such as temperature, food and water. Related sexual interest and behaviors are expressed and accepted only during this period. Female seasonal breeders will have one or more estrus cycles only when she is "in season" or fertile and receptive to mating. At other times of the year, they will be anestrus. Similarly, male seasonal breeders may exhibit changes in testosterone
Testosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
levels, testes weight and fertility depending on the time of year.
Seasonal breeders are distinct from opportunistic breeders
Opportunistic breeders
Flexible or opportunistic breeders mate whenever the conditions of their environment become favorable. Their ability and motivation to mate are primarily independent of day-length and instead rely on cues from short-term changes in local conditions like rainfall, food abundance and temperature...
, which mate whenever the conditions of their environment become favorable, and continuous breeders like humans that mate year-round.
Physiology
The hypothalamusHypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
is considered to be the central control for reproduction. Hence, factors that determine when a seasonal breeder will be ready for mating affect this tissue. This is achieved specifically through changes in the production of the hormone GnRH. GnRH in turn transits to the pituitary where it promotes the secretion into the bloodstream of the gonadotropin
Gonadotropin
Gonadotropins are protein hormones secreted by gonadotrope cells of the pituitary gland of vertebrates. This is a family of proteins, which include the mammalian hormones follitropin , lutropin , placental chorionic gonadotropins hCG and eCG and chorionic gonadotropin , as well as at least two...
LH
LH
LH, Lh, or lh may stand for:*Laurel and Hardy*Leasehold *Left-handed or left hand*Letterhead, the heading at the top of a sheet of letter paper*lh, a digraph for many languages...
, a pituitary hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
critical for reproductive function and behavior. Changes in gonadotropin secretion initiate the end of anestrus in females.
Photoperiod
When a seasonal breeder is ready for mating is strongly regulated by length of day (photoperiod) and thus season. Photoperiod likely affects the seasonal breeder through changes in melatoninMelatonin
Melatonin , also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants, and microbes...
secretion by the pineal gland
Pineal gland
The pineal gland is a small endocrine gland in the vertebrate brain. It produces the serotonin derivative melatonin, a hormone that affects the modulation of wake/sleep patterns and seasonal functions...
that ultimately alter GnRH release by the hypothalamus.
Hence, seasonal breeders can be divided into groups based on when they are fertile. "Long day" breeders cycle when days get longer (spring) and are anestrus in fall and winter. "Short day" breeders cycle when the length of daylight shortens (fall) and are anestrus in spring and summer. Domestication has allowed cattle and swine to be liberated from breeding seasonality.
Day length variations with latitude can also impact breeding. For instance, sheep and goats in tropical climes may breed throughout the year while those in more polar arctic areas may have a shortened season.
Females are generally more sensitive to changes in day length. For instance, unlike mares, stallions remain fertile year-round, suffering only some declines in sexual behavior and sperm production
Spermatogenesis
Spermatogenesis is the process by which male primary germ cells undergo division, and produce a number of cells termed spermatogonia, from which the primary spermatocytes are derived. Each primary spermatocyte divides into two secondary spermatocytes, and each secondary spermatocyte into two...
out of season.
Other Factors
Other factors that affect breeding time include the presence of a ready and available mate. For instance, the presence of a fertile male will induce an estrus cycle in a doe shortly after introduction.Further environmental factors can include nutrition, chemosensory and hormonal cues. Weight and age are other factors.
Partial list of seasonal breeders
Many non-mammals are seasonal breeders, such as many birds and fishFish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
. Here is partially listed those that are mammals.
Summer breeders
- Ruffed lemurRuffed lemurThe ruffed lemurs of the genus Varecia are strepsirrhine primates and the largest extant lemurs within the family Lemuridae. Like all living lemurs, they are found only on the island of Madagascar...
(May - July) - Select speciesSpeciesIn biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of hamsterHamsterHamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera....
, voleVoleA vole is a small rodent resembling a mouse but with a stouter body, a shorter hairy tail, a slightly rounder head, smaller ears and eyes, and differently formed molars . There are approximately 155 species of voles. They are sometimes known as meadow mice or field mice in North America...
and mouseMouseA mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...