2012 COURSE DATES: AUGUST 4 – 17, 2012 - Sirenian International

Reduced Belize manatee dispersal and genetic variation M. E. Hunter et al.
Driscoll et al., 2002). Examples of species with lower
diversity than the Belize manatee include the Mediterranean
monk seal (HE=0.41, NA=2.3, 15 loci; Paster et al., 2004)
and the critically endangered Amur leopard (H E=0.37,
NA=2.6, 25 loci; Uphyrkina et al., 2002).
The Belize population was also found to have reduced
variation compared with other marine mammal populations.
Trichechus manatus latirostris currently has greater diversity
and a quickly recovering large population, possibly owing to
a shorter and/or less intense bottleneck period. Hunting of
other marine mammal populations, such as the large cetaceans,
occurred for a similar duration and intensity as for the
Antillean manatee, and also resulted in the commercial
extinction of many populations in the 1800s or 1900s.
Populations with intense hunting and smaller historical
sizes, such as the North Atlantic right whale (NARW), appear
to have lost much of their diversity. The NARW was hunted
for an extended period (11th–20th century) and was reduced
from 12 000 individuals to the low hundreds, where it
remains today (Waldick et al., 2002). The NARW genetic
diversity reflects the extended and severe bottleneck the
population has endured (NA=4.1, HE=0.46, 11 polymorphic
loci). Alternatively, the related South Atlantic right
whale population experienced less intense whaling that allowed
the population to remain in the thousands and has
higher genetic diversity (Waldick et al., 2002). Genetic studies
have found large diversity, pre-whaling population estimates
and recovered population sizes for fin (Berube et al., 1998),
minke (Pastene, Goto & Kanda, 2009) and humpbacks whales
(Garrigue et al., 2004), and suggest that the cessation of
hunting in the early 20th century, allowed these populations
to remain above 1000 individuals (Roman & Palumbi, 2003).
Though it is reported as once being abundant in the
Caribbean, T. m. manatus historical population sizes were
not likely as large as some whale populations (Husar, 1977,
1978). Further, a protracted period of severe hunting reduced
the regional populations to o1000 individuals and in
598
Figure 4 Plot of posterior probability of assignment
for individuals (vertical lines) based
on Bayesian analysis of variation at 16 microsatellite
loci. Individuals are grouped by population,
(a) Belize and Florida and (b) the Belize
City Cayes and Southern Lagoon System. Red
indicates genetic cluster 1 and green indicates
genetic cluster 2 in each plot.
some cases to effective extinction (O’Shea & Salisbury, 1991;
UNEP/CEP, 1995). This population contraction could have
reduced the genetic diversity in Belize, which is below even
that of the critically endangered NARW. However, lower
dispersal and immigration capabilities in manatees may
limit the exchange and development of inherent diversity in
the taxa.
The detected heterozygosity excess, mean pairwise values,
and recent reduction in the population size suggests that a
bottleneck/founder event, inbreeding, genetic drift and/or a
reproductive skew has increased the relatedness among
Belize manatees. Because diversity is considered necessary
for adaptation to diseases and environmental changes,
erosion of the currently low variation could negatively affect
the population in the future (Reusch & Wood, 2007).
Populations characterized by low diversity and past inbreeding
are at risk for further losses and those not intensely
monitored can become inbred with little warning (Frankham,
1995; Bijlsma, Bundgaard & Boerema, 2000). Alternatively,
inbreeding accumulating gradually in populations
can provide the opportunity for natural selection to remove
deleterious alleles. To date, there are no indications of
decreased fitness due to inbreeding depression in the Belize
population. However, further reduction of population size
could increase inbreeding above the ‘inbreeding threshold,’
resulting in loss of fitness and risk of extinction (Frankham,
1995). Further monitoring could help to detect inbreeding
depression or declines in population size (Schwartz, Luikart
& Waples, 2007).
The immigration of genetically distinct individuals can
substantially reduce the deleterious effects of inbreeding
(Frankham et al., 2002). However, the enhancement of
diversity through this mechanism is limited since many
manatee populations are small, isolated and movement is
restricted by their dependence on fresh water. Manatees
prefer near-shore habitat, have limited coastal ranges and
infrequently move long distances, highlighting the need for
Animal Conservation 13 (2010) 592–602 c 2010 The Authors. Animal Conservation c 2010 The Zoological Society of London