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Call for a paradigm shift in the genetic management of fragmented…
Call for a
paradigm shift
in the
genetic management of fragmented populations
---Genetic rescue
how: The good news is that the negative effects of inbreeding and low genetic diversity can often
be reversed by
crossing at-risk populations with genetically distinct ones,
But why Genetic rescue has been so rare:
that mixing gene-pools will cause
outbreeding depression
(loss of fitness when
populations that are too genetically different are crossed.
Fears of outbreeding depression are exaggerated
Loss of local adaptation
is also usually a minor and manageable issue. Many small
populations will not be well-adapted to their current environment
Even if
local adaptation might be substantive.
, its loss can be prevented by
careful planning
, as was done in the case of the
Florida panther
We recommend the use of species concepts
based on
reproductive isolation,
(The mechanisms of
reproductive isolation
are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring are sterile.)
Step 3 involves
screening for a high risk of outbreeding depression,
using the decision tree in
Frankham et al. (2011)
The occurrence of
outbreeding depression
is
largely predictable
:
populations that are chromosomally compatible, were isolated by human activities within the
last 500 years, and a
re not adapted to strongly different environments are at very low risk of
outbreeding depression when crossed
Step 2 asks if there is
another population to which the inbred population can be crossed
al. 2016). Attempting passively to preserve this random
uniqueness, rather than instituting active genetic management, increases extinction risk.
Step 4 addresses the probable magnitude of
the genetic rescue effect
If a naturally outbreeding species of conservation concern has several geographically separate
populations, we should
first determine if any are small, genetically isolated, and inbred
An inbreeding level of 10% may
sound like a low threshold for intervention, but in fact it represents a very considerable loss
of fitness.
If a population is likely to
benefit from augmented gene flow, managers should
consider active genetic management
(Step 5).
Cultural concerns about gene-pool mixing center on preserving taxonomic integrity: fear that
the
rescued population will be different after rescue
Why: Continuing human destruction and fragmentation of habitats worldwide necessitates
management interventions based on evolutionary theory to preserve populations of threatened
plants and animals
why: We have to use genetic management, because
inbreeding and genetic variation
have become two main issues
Outcome
: However. Presently, most governments stress
preserving
genetic uniqueness and taxonomic integrity.
This outdated
approach is not scientifically justifiable,
may promote the preservation of traits associated
with inbreeding depression (e.g., the characteristic
Moving some individuals or their gametes will be better than moving none
; however, if
molecular genetic data or pedigrees exist,
decisions should be guided quantitatively by mean
kinship at the population or individual level
Minimizing mean kinship (also called coancestry
)
minimizes inbreeding in the next generation, and maximizes the retention of genetic
diversity (Ballou & Lacy 1995). C
Sgrò 2011). In the most severe cases, it
may be necessary to
cross a population to a related species, or translocate individuals to a
location outside of the species‟ historic range.