Seasonal Timing of Reproduction and
Follicular Development of the
Recently Introduced Boa constrictor on
Aruba, Dutch West Indies
William I. Lutterschmidt1 Everett D. Wilson1 Howard K. Reinert2
Melissa A. Miller1 R. Andrew Odum3
1Department
of Biological Sciences, Sam Houston State University, Huntsville,
Texas, USA
2Department of Biology, The College of New Jersey, Ewing, New Jersey, USA
3Department of Herpetology, Toledo Zoological Society, Toledo, Ohio, USA
Why Study Reproduction?
Why Study Reproduction?
Why Study Reproduction?
Why Study Reproduction?
The documented increase in the Boa constrictor population on Aruba since 1999.
Although a large population growth was observed between 1999 and 2003, the
population may have reached its carrying capacity as indicated by the fluctuation in
the number of snakes between 2003 and 2006.
FAC T O R S F O R S U C C E S S ?
 A generalist feeder (Quick et al. 2005) there is the potential for
increased potential for survive and for becoming permanently
established.
 The reproductive life history of Boa constrictor favors survival
because females give birth to live young via ovoviviparity. This may
increase fitness by increasing the chance of offspring survival.
METHODS
 Preliminary data were collected from 136 euthanized snakes
(71males and 65 females) collected from the island of Aruba over the
months January through July and November and December. (Now a
complete data set for future analyses consists of 292 snakes sampled
from all months).
 Ovarian follicles within the oviductal tissue and testes were removed
from a ventral incision, fixed in 10% formalin, and stored in 70%
ethanol (Lutterschmidt et al. 2005; Lutterschmidt et al. 2006).
METHODS
 Preliminary reproductive data (clutch size and mass, follicle length,
and testes mass, length and width) and morphological data (Mb, SVL)
were recorded.
 Digital calipers were used to determine follicle diameter and testes
length and width. Follicles were grouped according to a standard
classification system developed by Betz (1963).
Class I = 0.1 - 5.0 mm
Class II = 5.1 - 10.0 mm
Class III = 10.1 - 20.0 mm
Class IV = 20.1 - 46.0 mm
 Follicle size was compared among months and regressed against
female Mb to determine if there is a relationship between body size
and follicle size (Kofron 1979, Kofron 1983, Holycross and Goldberg
2001, Rosen and Goldberg 2002, Goldberg 2002).
QUESTIONS
 What is the observed sex ratio of Boa constrictor on Aruba?
 What proportion of female snakes are reproductive?
 How large are female snakes when they become reproductive?
 What is the reproductive timing of Boa constrictor on Aruba?
 When do snakes mate?
 When do female snakes give birth to young?
 Does reproductive timing coincide with the reproductive timing
of the Aruba Island Rattlesnake (Crotalus unicolor) and is there
potential for concern?
QUESTIONS
 What is the observed sex ratio of Boa constrictor on Aruba?
Based on the preliminary data of 136 snakes, we found nearly a 50:50
male to female sex ratio (actual ratio = 52.3 : 47.8).
The entire sample of 292 snakes showed a similar, but reversed sex
ratio where a greater proportion of females were sampled (male :
female sex ratio = 47.6 : 52.4).
QUESTIONS
 What proportion of female snakes are reproductive?
 Follicles may or may not develop into eggs or embryos
 development of eggs and embryos depend largely on food
availability which will directly influence female body size and
body condition.
Out of 153 females, 94 females (61%)
had developed follicles
A
B
C
D
QUESTIONS
 How large are female snakes when they become reproductive?
Of the gravid or post-parturition individuals examined by necropsy
mean body mass (Mb) was 2.15 kg (SE = 0.093, n = 14) and ranged
from 0.854 kg to 5.00 kg.
Female Mb also influenced both follicle size and the number of
developing follicles.
120
F = 26.12; df = 1, 63
P < 0.001, r2= 0.293
50
100
40
Clutch Size
Mean Follicle Length (mm)
60
30
20
10
0
80
60
40
20
F = 18.511; df = 1, 63
P< 0.001; r2= 0.227
0
0
1
2
3
4
5
Body
M Mass
(kg)(kg)
b
6
7
8
80
100
120
140
160
180
200
SVL(cm)
SVL
220
240
260
QUESTIONS
 What is the reproductive timing of Boa constrictor on Aruba?
 When do snakes mate?
 When do female snakes give birth to young?
Based on field observations of snakes with the use of radiotelemetry, we
believe that females may be receptive in February and March.
Based on the necropsy of snakes, we found a female with large eggs on 8
August, two females with embryos on 21 July and 31 August, and several
females that appeared to be post-parturition in September and October.
QUESTIONS
 Does reproductive timing coincide with the reproductive timing
of the Aruba Island Rattlesnake (Crotalus unicolor) and is there
potential for concern?
This is a most important question which will require further investigation.
However, if the reproductive timing of parturition does overlaps between Boa
constrictor and Crotalus unicolor, there is the potential for concern.
Why? If these neonates require and use similar microhabitats, there may be
substantial niche overlap for resources, including food. Such competition
between species could influence the future success of Crotalus unicolor.
Niche overlap
Habitat Relationship between Boas and Cascabels
Multivariate Habitat Overlap = 26%
ACKNOWLEDGEMENTS
Arikok National Park Foundation
Department of Agriculture, Husbandry and Fisheries
Department of Veterinary Services
The College of New Jersey
Sam Houston State University
Toledo Zoological Society
Albo Aruba
Valero
Meta Corp
AHATA
La Cabana
Renaissance
Talk of the Town
Amsterdam Manor
Holiday Inn
Playa Linda