size and overall reproductive output (Chown and Klok 2003). Prolonged development is achieved either by increasing instar numbers or by extending instar
growth over 2 years, which involves passing from pluri- or univoltinism in lowlands, to semivoltinism in highlands, with individuals overwintering at different
instar stages over the years (Miles et al. 1997), or entering diapause at different
stages (Dingle et al. 1990).
The allometric reduction in egg number with elevation is often accompanied by
increased egg size to enhance embryo viability at low temperatures, whereas, at
higher temperatures, it pays off to produce more and smaller eggs since offspring
mortality is lower (Fischer et al. 2003). Increased adult survival with elevation has
been observed in fruit flies (Duyck et al. 2010) and is explained by trade-offs
between fecundity and longevity (Norry et al. 2006) or increasing rates of damage
from by-products of metabolism in hot temperatures (Leiser et al. 2011). In annual
species, however, selection on reproductive schedules may induce the opposite
patterns, with accelerated senescence at the completion of reproduction (Tatar et al.
1997).
Asexual, or parthenogenetic, populations frequently appear in high-altitude
habitats. This strategy, favoured in areas with few sexual competitors (Peck et al.
1998), permitted persistence in isolated ice-free summits surrounded by glaciers
(‘nunataks’) during the Pleistocene glaciation periods (Wachter et al. 2012).
The optimal life strategies of crustaceans also vary along elevation, and females
from stream head or alpine waters, for instance, lay larger eggs but smaller clutches
than those from lowlands (decapods: Hayashi and Hamano 1984; Mashiko 1990;
Hancock et al. 1998; amphipods: Wilhelm and Schindler 2000). Among arachnids,
alpine tundra Pardosa wolf spiders display no interpopulation variation in egg
number per cocoon, but generation time is twofold than that in lowlands (Schmoller
1970).
11.4.2 Fishes
Despite the high thermal conductivity of water buffers thermal fluctuations over
time and space, and thus reduces the opportunities for sharp temperature-driven
selection, temperature has a pervasive influence on developmental traits of fishes
and adaptation to local thermal regimes as well as plastic responses are well documented (Haugen and Vøllestad 2000). Factors such as water flow or predation risk
also affect fish life-history decisions and, in particular, recruitment is a key trait in
determining fish allocation to contrasting life-history traits. As a general rule, larger
sizes, later maturity and long reproductive lifespans are selected for when recruitment is low (Kennedy et al. 2003; Parra et al. 2014). Sternberg and Kennard (2013)
found that among Australian freshwater fishes, egg guarding species that reach
maturity at a small size were more frequent in environments with perennial flow
and low mean annual temperatures typical of uplands. Conversely, larger-bodied,
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growth over 2 years, which involves passing from pluri- or univoltinism in lowlands, to semivoltinism in highlands, with individuals overwintering at different
instar stages over the years (Miles et al. 1997), or entering diapause at different
stages (Dingle et al. 1990).
The allometric reduction in egg number with elevation is often accompanied by
increased egg size to enhance embryo viability at low temperatures, whereas, at
higher temperatures, it pays off to produce more and smaller eggs since offspring
mortality is lower (Fischer et al. 2003). Increased adult survival with elevation has
been observed in fruit flies (Duyck et al. 2010) and is explained by trade-offs
between fecundity and longevity (Norry et al. 2006) or increasing rates of damage
from by-products of metabolism in hot temperatures (Leiser et al. 2011). In annual
species, however, selection on reproductive schedules may induce the opposite
patterns, with accelerated senescence at the completion of reproduction (Tatar et al.
1997).
Asexual, or parthenogenetic, populations frequently appear in high-altitude
habitats. This strategy, favoured in areas with few sexual competitors (Peck et al.
1998), permitted persistence in isolated ice-free summits surrounded by glaciers
(‘nunataks’) during the Pleistocene glaciation periods (Wachter et al. 2012).
The optimal life strategies of crustaceans also vary along elevation, and females
from stream head or alpine waters, for instance, lay larger eggs but smaller clutches
than those from lowlands (decapods: Hayashi and Hamano 1984; Mashiko 1990;
Hancock et al. 1998; amphipods: Wilhelm and Schindler 2000). Among arachnids,
alpine tundra Pardosa wolf spiders display no interpopulation variation in egg
number per cocoon, but generation time is twofold than that in lowlands (Schmoller
1970).
11.4.2 Fishes
Despite the high thermal conductivity of water buffers thermal fluctuations over
time and space, and thus reduces the opportunities for sharp temperature-driven
selection, temperature has a pervasive influence on developmental traits of fishes
and adaptation to local thermal regimes as well as plastic responses are well documented (Haugen and Vøllestad 2000). Factors such as water flow or predation risk
also affect fish life-history decisions and, in particular, recruitment is a key trait in
determining fish allocation to contrasting life-history traits. As a general rule, larger
sizes, later maturity and long reproductive lifespans are selected for when recruitment is low (Kennedy et al. 2003; Parra et al. 2014). Sternberg and Kennard (2013)
found that among Australian freshwater fishes, egg guarding species that reach
maturity at a small size were more frequent in environments with perennial flow
and low mean annual temperatures typical of uplands. Conversely, larger-bodied,
262
P. Laiolo and J.R. Obeso