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, USA2Department 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.

F A C 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.

M E T H O D S

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).

M E T H O D S

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).

Q U E S T I O N S

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?

Q U E S T I O N S

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).

Q U E S T I O N S

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

DC

BA

Q U E S T I O N S

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.

Body Mass (kg)

0 1 2 3 4 5 6 7 8

Me

an

Fo

llic

le L

en

gth

(m

m)

0

10

20

30

40

50

60

Mb (kg)

F = 26.12; df = 1, 63

P < 0.001, r2= 0.293

SVL

80 100 120 140 160 180 200 220 240 260

Clu

tch

Siz

e

0

20

40

60

80

100

120

SVL (cm)

F = 18.511; df = 1, 63

P< 0.001; r2= 0.227

Q U E S T I O N S

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.

Q U E S T I O N S

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.

Habitat Relationship between Boas and Cascabels

Niche overlap

Multivariate Habitat Overlap = 26%

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

A C K N O W L E D G E M E N T S