Mating opportunities and energetic constraints drive variation in age-dependent sexual signalling

When males repeatedly produce energetically expensive sexual signals, trade-offs between current and future investment can cause plasticity in age-dependent signalling. Such variation is often interpreted as alternate adaptive strategies: live fast and die young vs. slow and steady.  An alternative (yet rarely tested) explanation is that condition-dependent constraints on allocation cause variation in signalling with age (‘late bloomers’ do not have early investment options). Testing this hypothesis is challenging because resource acquisition and allocation are difficult to measure, and energetic reserves both affect and are affected by reproductive effort.  We simultaneously manipulated acquisition (through dietary nutrition) and access to potential mates (as a proxy for manipulating sexual trait allocation) in male decorated crickets (Gryllodes sigillatus), while measuring age- and signalling effort-mediated changes in energy storage components.  Increased diet quality caused increased signalling effort and energy storage, while access to females increased both the likelihood of and time spent signalling. Males with lower resource budgets signalled less, but still suffered energetic storage loss and viability costs.  Our results suggest that energetic constraints, rather than strategic resource accumulation, reduced signalling levels in males with lower resource acquisition ability. Our findings imply a non-adaptive explanation for age-dependent variation in sexual signalling, and an important role for energetic constraints in maintaining the honesty of costly behavioural displays

Genetic variance in fitness indicates rapid contemporary adaptive evolution in wild animals

The rate of adaptive evolution, the contribution of selection to genetic changes that increase mean fitness, is determined by the additive genetic variance in individual relative fitness. To date, there are few robust estimates of this parameter for natural populations, and it is therefore unclear whether adaptive evolution can play a meaningful role in short-term population dynamics. We developed and applied quantitative genetic methods to long-term datasets from 19 wild bird and mammal populations and found that, while estimates vary between populations, additive genetic variance in relative fitness is often substantial and, on average, twice that of previous estimates. We show that these rates of contemporary adaptive evolution can affect population dynamics and hence that natural selection has the potential to partly mitigate effects of current environmental change

Mapping binding sites for the PDE4D5 cAMP-specific phosphodiesterase to the N- and C-domains of beta-arrestin using spot-immobilized peptide arrays

Beta2-ARs (beta2-adrenoceptors) become desensitized rapidly upon recruitment of cytosolic beta-arrestin. PDE4D5 (family 4 cAMP-specific phosphodiesterase, subfamily D, isoform 5) can be recruited in complex with beta-arrestin, whereupon it regulates PKA (cAMP-dependent protein kinase) phosphorylation of the beta2-AR. In the present study, we have used novel technology, employing a library of overlapping peptides (25-mers) immobilized on cellulose membranes that scan the entire sequence of beta-arrestin 2, to define the interaction sites on beta-arrestin 2 for binding of PDE4D5 and the cognate long isoform, PDE4D3. We have identified a binding site in the beta-arrestin 2 N-domain for the common PDE4D catalytic unit and two regions in the beta-arrestin 2 C-domain that confer specificity for PDE4D5 binding. Alanine-scanning peptide array analysis of the N-domain binding region identified severely reduced interaction with PDE4D5 upon R26A substitution, and reduced interaction upon either K18A or T20A substitution. Similar analysis of the beta-arrestin 2 C-domain identified Arg286 and Asp291, together with the Leu215-His220 region, as being important for binding PDE4D5, but not PDE4D3. Transfection with wild-type beta-arrestin 2 profoundly decreased isoprenaline-stimulated PKA phosphorylation of the beta2-AR in MEFs (mouse embryo fibroblasts) lacking both beta-arrestin 1 and beta-arrestin 2. This effect was negated using either the R26A or the R286A mutant form of beta-arrestin 2 or a mutant with substitution of an alanine cassette for Leu215-His220, which showed little or no PDE4D5 binding, but was still recruited to the beta2-AR upon isoprenaline challenge. These data show that the interaction of PDE4D5 with both the N- and C-domains of beta-arrestin 2 are essential for beta2-AR regulation