Download Galapagos Marine Iguana Reproductive Cycle in Captive Breeding

Galapagos Marine Iguana Reproductive Cycle in
Captive Breeding
Cathleen O’Brien and Selestia Tomlinson
April 5, 2006
Dr. John Kastelic
Biology 3850N
Captive breeding programs are practiced in zoos and sanctuaries around the world
to conserve, educate and research species. By establishing captive populations,
endangered species have a better chance of not going extinct (National Zoo, 2006). In
fact, many species can attribute their continuing existence to captive breeding programs,
such as black-footed ferrets (National Zoo, 2006). The ultimate goals of captive breeding
are to maintain a healthy age structure, to protect a population against disease, assurance
that that reproduction is reliably successful and to preserve the gene pool so problems
with inbreeding can be avoided (Fritts et. al. 2000). Often reintroduction of animals
back into the wild is also a focus of this program.
The Galapagos iguana is an ideal candidate for a captive breeding program
because they are classified as vulnerable and according to the World Conservation Union
they are a red listed species (IUCN, 2006). They are the only marine iguanas in the
world and inhabit an environment where no mammalian predators live (IUCN, 2006).
There are some noticeable difference between marine iguanas in the wild and
those in captivity (Albers, 1993). The weight of those in captivity is comparatively much
larger than compared to those in the wild, sometimes up to. Also, in the wild the
availability of suitable food is the main factor that contributes to the timing of egg
hatching (Albers, 1993). When in captivity there is an abundance of food available to
them at all times, therefore they are often confused by when exactly they should be
mating and when the eggs should be hatching (Albers, 1993). When in captivity there is
a higher frequency of soft shelled eggs and these eggs never hatch so this is
representative of yet another limitation captive breeding has (Albers, 1993).
There is a significant diversity of species amongst the islands with major
differences in size, colour and seasonality (National Zoo, 2006). There has been genetic
studies done in order to determine relationships among populations and evolutionary
out groups (Fritts et. al. 2000). Marine iguanas have demonstrated a greater variation in
DNA from the mitochondria than from the cell nucleus (Fritts et. al, 2000). This suggests
those different migratory patterns between males and females exist (Fritts et. al. 2000).
The steroid hormone patterns and aggression during breeding is different in
female Galapagos marine iguanas (Rubenstein and Wikelski, 2005). Usually, males are
the protecting sex against other predators but females in this species is the protectors of
their nesting sites (Rubenstein and Wikelski, 2005).In a captive breeding system, a study
explains the hormones levels of the female Galapagos marine iguanas (Rubenstein and
Wikelski, 2005). During the mating and nesting periods, the changes in levels of
testosterone, estradiol, corticosterone, and progesterone will be discussed.
During the breeding phases, testosterone was higher during the last copulation of
the mating period, as this is related to female-male aggression (Rubenstein and Wikelski,
2005). While in the nesting period, it increases in the digging and covering stage
(Rubenstein and Wikelski, 2005).
The estradiol hormone supports aggressive behavior in female reptiles and it may
control the same thing in pregnant and lactating mammals, but suppress it in sexually
receptive mammals (Rubenstein and Wikelski, 2005). It is increased more in the mating
period and there is a chance that it is increased from pre-mating stage to the copulation
stage and remains elevated throughout the mating stages (Rubenstein and Wikelski,
2005). During the nesting period, females have estradiol levels above the detection limit
in the study (Rubenstein and Wikelski, 2005).
The hormone corticosterone is lower in the mating period and begins to rise at the
end of the mating stage (Rubenstein and Wikelski, 2005). It is at the highest elevation
rate before the eggs are laid, but declines significantly immediately after egg laying
(Rubenstein and Wikelski, 2005).
Progesterone levels are similar during both mating and nesting periods
(Rubenstein and Wikelski, 2005). The hormone is higher at the beginning of the mating
period, but decreasing towards the end of the stage (Rubenstein and Wikelski, 2005).
The beginning of the nesting stage has an increased amount of progesterone and declines
steadily throughout (Rubenstein and Wikelski, 2005).
The following chart shows the levels of hormones at the mating and nesting
periods. The hormones that are illustrated in Figure 1.0 are testosterone, estradiol,
corticosterone, and progesterone.
Figure 1.0 Hormone Levels for Testosterone (A), Estradiol (B), Corticosterone (C), and (D) Progesterone
in Female Galapagos Marine Iguanas during the Mating Stage (black bars) and Nesting Stage (white bars).
In the mating period, the hormones that are increased are testosterone, estradiol,
progesterone and corticosterone is at a much lower level. During the nesting period,
corticosterone and progesterone is increased, while testosterone and estradiol are
decreased to lower levels.
Females alter their behavior by elevating their posture and head bobbing
aggressively to selected males to signal that they are ready to mate (Wikelski et. al.
1995). Mating occurs in the month of February (Wikelski et. al. 1995). After mating has
ended and females have moved to the nesting areas, they are extremely aggressive against
other females that are trying to steal or defend their nest site. (Wikelski et. al. 1995).
Females defend nest sites for a mean of three days before and a mean of five days after
egg laying (Wikelski et. al, 1995).
General human interest plays a role in the captive breeding program as well. A
zoo is a business and wants to attract visitors and therefore might consider captive
breeding programs for animals that attract a high number of visitors. On the other hand,
by breeding an animal that is not as well known about the public might be enticed to
become more interested and thus helping the long term outlook of the species.
The overall success of a captive breeding program is dependent on many factors.
Extensive time, money and labour is invested to ensure that the genetic diversity is great
and survival rates high (Fritts, 2000). However, despite the best efforts put forward by
humans, technology and science it is the animal itself that holds the key to the ultimate
success of these programs.
Cited Literature
Albera, Koen. (1993) Reproductive Adaptations of Green Iguana on a Semiarid Island.
Capeia, Vol. 1978, No.3, pp. 790-798.
Balmford, A., Mace, G., et al. (1996). Designing the Ark: Setting Priorities for Captive
Breeding. Conservation Biology. Vol. 10, No.3, pp. 719-727.
Bock, Brian. (1989). Nesting Season Movements of Female Green Iguanas in Panama.
Capeia. Vol. 1989, No.1, pp.214-216.
Conservation and Science. (2006). Endangered Species Science: Captive Breeding.
Retrieved on April 1, 2006 from www.nationalzoo.si.edu/ConservationAndScience.org.
Fritts, H.L., Snell, L. et al. (2000) Progress and Priorities in Research for the
Conservation of Reptiles. Science for Conservation in the Galapagos.
Green Iguana Society. (2004). Breeding Iguanas in Captivity. Retrieved on April 1, 2006
from www.greenigsociety.org/breeding.htm.
Rand, Stanley. (1968) A Nesting Aggregation of Iguanas. Capeia. Vol. 1978, No.3,
pp.552-561.
The World Conservation Union. 2006. Retrieved on March 23, 2006 from www.iucn.org.
Trillmich, F., and Trillmich, KGK. (1984). The Mating Systems of Pinnipeds and Marine
Iguanas: Convergent Evolution of Polygyny. Biological Journal of the Linnean Society.
Wilelski, M., Carbone, C., and Trillmich, F. (2002) Lekking in Marine Iguanas: Female
Grouping and Male Reproductive Strategies. Evolution. Vol. 51, No. 3, pp. 922-936.