Life-history variation in reptiles reflects natural selection on energy allocation to growth, survival, and reproduction strategies across heterogeneous environments. Along latitudinal and elevational gradients, populations often diverge in maternal investment and in the maternal effects shaping offspring phenotype at birth, consistent with both local adaptation and phenotypic plasticity (Doughty 1996; Bonnet et al. 2000; Kratochvíl and Frynta 2006; Uusi-Heikkilä et al. 2012; Slavenko et al. 2019).

Elevational gradients provide powerful natural experiments because they generate predictable shifts in temperature regimes, season length, food availability, and predation pressure, thereby shaping activity seasons and the time window available for reproduction (Grant and Dunham 1990; Mathies and Andrews 1995; Zamora-Camacho et al. 2013). In response to these environmental shifts, populations are expected to diverge in reproductive traits and strategies (Ballinger 1979; Meiri et al. 2020; Wise and Jaeger 2021). For example, in cold environments, reproductive females may partially buffer embryos from suboptimal or variable thermal conditions through behavioural thermoregulation and microhabitat selection (i.e., maternal manipulation), thereby influencing developmental trajectories and offspring phenotype (Le Henanff et al. 2013; Feldman et al. 2016). However, these patterns are not universal because elevation integrates multiple ecological dimensions, and reproductive responses are constrained by lineage-specific traits, including transitions to viviparity (Shine 1983; Blackburn 2000). Thus, many oviparous lineages persist in cold environments and may instead adjust nesting behaviour (e.g., Blouin-Demers et al. 2004; Pike et al. 2010), reproductive timing (e.g., Olsson and Shine 1997; Warner and Shine 2007), and egg provisioning (e.g., Deme et al. 2022) to cope with thermal and seasonal limitations.

In oviparous reptiles, female body size often predicts reproductive investment because it constrains abdominal volume and energetic capacity, thereby shaping egg size, clutch size, or both (Bonnet et al. 2000; Kratochvíl and Frynta 2006; Martins et al. 2022; Lourdais et al. 2024). This size dependence is particularly relevant in taxa with invariant clutch size, where the classical offspring size–number trade-off is expressed primarily through egg size rather than clutch size (Goodman 2006; Kratochvíl and Frynta 2006). In geckos (clade Gekkota), egg dimensions and mass can vary among females, populations, and environments, providing a key pathway through which mothers modulate offspring traits (Sakai 2021). Egg size, in turn, is a major determinant of hatchling size and condition, with potential consequences for early energy reserves, growth, and survival (VanDamme et al. 1992; Iraeta et al. 2006; Le Henanff et al. 2013). Understanding how elevation and maternal size jointly shape egg provisioning therefore offers a mechanistic link between environmental gradients and early-life fitness components.

The Atlas Day Gecko, Quedenfeldtia trachyblepharus (Boettger, 1873), is a cold-adapted, diurnal gecko whose activity and reproduction are constrained by seasonal thermal conditions in the High Atlas Mountains of Morocco (Bouazza et al. 2016). Early in the activity season, field body temperatures are typically below the preferred range (T_pref ≈ 29.5–31.5 °C), whereas individuals reach or remain within T_pref mainly in late spring (Bouazza et al. 2016). The species occurs from approximately 1,400 m to > 4,000 m, offering a natural gradient for testing how high-mountain conditions shape variation in maternal traits and egg provisioning. Although elevational divergence in reproductive traits has been documented in several lizard clades (Mathies and Andrews 1995; Iraeta et al. 2006; Rodríguez-Díaz and Braña 2012; Deme et al. 2022), few studies have examined variation in egg and hatchling traits across elevation in oviparous geckos with invariant clutch size.

Here, we examine how maternal body size and elevation of origin jointly relate to reproductive traits in Q. trachyblepharus. We quantified egg mass, egg volume, and relative clutch mass (RCM) in females sampled across five elevation classes (1,900–3,000 m) in the High Atlas Mountains and tested whether elevation explains variation in these traits. To link maternal investment to early offspring traits, we also measured hatchling size and body condition after incubation under standardized laboratory conditions. Our main question is whether high-elevation environments are associated with shifts in maternal size and/or per-offspring investment (egg traits), and whether such shifts translate into predictable variation in hatchling traits. We predicted that (i) consistent with Bergmann’s rule, females from higher elevations would exhibit larger body size and enhanced body condition. Given the invariant clutch size of geckos, we further predicted that (ii) maternal investment–egg mass, egg volume, and relative clutch mass (RCM) would vary among elevations, reflecting increased per-offspring investment under the shorter activity seasons and thermal constraints characteristic of high-altitude environments.

Our results revealed significant among-population differences in maternal body size, egg size, and relative clutch mass (RCM) in Quedenfeldtia trachyblepharus along an elevational gradient. Our finding that high-elevation females produced larger and heavier eggs is consistent with our predictions. These findings also suggest that females increase per-offspring investment in high-elevation populations, likely reflecting environmental differences along the gradient.

Maternal body size increased with elevation, consistent with previous work showing that Q. trachyblepharus from higher altitudes tend to have larger body size, because higher elevation habitats provide this alpine gecko with a sort of “refuge” from competition, allowing for greater maternal investment to ensure better body conditions (Comas et al. 2014; Comas 2020). Geographic patterns in lizard body size are often related to local environmental conditions, and factors such as resource abundance may promote larger female body size, aligning with broader patterns linking growth and reproductive investment (Sebens 2003). In lizards, variation in maternal body size is influenced mainly by seasonal limitations of food resources, which can restrict growth (Adolph and Porter 1996; Iraeta et al. 2006). Alternatively, between-population variation in maternal body size may have evolved during adaptive radiation and changing climate conditions in different localities (Angilletta 2009).

Maternal body size is one of the primary traits that directly or indirectly influences life-history traits in organisms, leading to covariation among fitness-related traits, including egg traits (Kratochvíl and Frynta 2006; Slavenko et al. 2019; Wise and Jaeger 2021). In our study, egg mass and egg volume increased with maternal SVL, consistent with the positive association between maternal size and offspring quality reported in geckos and other lizards with fixed clutch size (Goodman 2006; Kratochvíl and Frynta 2006; Schwarz and Meiri 2017; Sakai 2021). However, relative clutch mass (RCM) declined with female size, indicating negative allometry in reproductive allocation. This relationship may make female reproductive output susceptible to age because lizards show indeterminate growth (Vitt and Congdon 1978; Shine 1992). In Q. trachyblepharus, however, maternal body size is not the only determinant of reproductive traits (egg mass/egg volume/RCM), because among-population differences in reproductive traits persisted after controlling for maternal SVL. Previous studies on lizard species have shown that variation in reproductive output can be site-specific, depending on the size of reproductive females and their energy storage capacity (Roitberg et al. 2013). Therefore, reproductive traits among populations of Q. trachyblepharus may be driven by the interplay between intrinsic factors (e.g., body size and age) and extrinsic factors (e.g., local environmental conditions) (Comas et al. 2014; Comas 2020).

As we predicted, females produced larger eggs at higher elevations, and egg traits were key predictors of hatchling phenotype. Hatchling size and body condition were positively associated with egg traits (egg mass and egg volume). Egg size is often a close proxy for the total resources allocated to embryonic development, which may influence neonatal condition (Le Henanff et al. 2013). Similar patterns have been observed in lizards with variable clutch size, where females produce smaller clutches of larger eggs at high elevations (Deme et al. 2022). These results are consistent with the idea that environmental constraints in the Atlas Mountains (e.g., low temperatures and short activity seasons) shift female reproductive allocation per offspring investment (i.e. from offspring quantity to offspring quality), when time for growth is limited and larger offspring gain survival or performance advantages (see Andrews et al. 2000; Uller and Olsson 2010; Le Henanff et al. 2013). In contrast, elevation did not explain additional variation in hatchling SVL or body condition once egg traits were considered, suggesting that elevational effects on hatchlings operate mainly through maternal provisioning rather than direct population differences in hatchling phenotype.

The observed elevational patterns in life-history traits may also be influenced by other biotic and abiotic factors associated with geographic distance between studied populations, beyond temperature directly linked to elevation. Unfortunately, we currently do not have detailed information on biotic factors such as prey availability and predation pressure for each population. Future work combining nest microclimate monitoring, maternal body condition, and incubation under fluctuating thermal regimes, followed by measurements of post-hatching growth and ecophysiological traits (e.g., early thermal preference and performance), would clarify the mechanisms and fitness consequences of increased egg size at high elevation (see Iraeta et al. 2006).

In conclusion, our findings highlight how maternal size-dependent allocation and elevational context jointly shape reproductive output in a high-mountain gecko. Larger eggs at high elevation, independent of maternal size, underscore the potential importance of maternal provisioning as a pathway linking environmental constraint to offspring traits. However, understanding whether these shifts along elevational gradients are driven only by environmental conditions or reflect genetically based local adaptation requires further investigation.