The small tortoises of southern Africa include the only testudinid taxa that produce single-egg clutches. This group includes the world's smallest tortoise, Homopus signatus (Gmelin, 1789), which inhabits a harsh, arid environment. Climate and body size may influence reproductive output, so we hypothesized that the east-west aridity gradient in southern Africa affects egg and clutch size of the small indigenous tortoises, and that the morphology of H. signatus constrains egg size, preventing the formation of optimal eggs. Here we show that aridity and unpredictable rainfall determine which of these tortoise taxa produce single-egg clutches. Taxa in less predictable environments produce larger eggs relative to body size than do taxa in more predictable environments. Homopus signatus produces the largest egg relative to body size, probably to enhance offspring survival in its harsh environment. Body size, pelvic aperture size, and the narrow anal gap of H. signatus appear to constrain egg size. Despite these constraints, females produce rigidshelled eggs larger than the pelvic canal and use pelvic kinesis to pass eggs at oviposition; both features are unknown in other chelonians and emphasize the selective advantage of large eggs to H. signatus. Résumé :Les petites tortues du sud de l'Afrique contiennent les seuls taxons de testudinidés qui produisent une seule couvée. Ce groupe comprend les plus petites tortues du monde, Homopus signatus (Gmelin, 1789), qui habitent des milieux rudes et arides. Comme le climat et la taille corporelle influencent vraisemblablement le rendement reproductif, nous avons émis l'hypothèse que le gradient est-ouest d'aridité dans le sud de l'Afrique affecte la taille des oeufs et celle des couvées des petites tortues indigènes et que la morphologie d'H. signatus limite la taille des oeufs, empê-chant ainsi la formation d'oeufs optimaux. Nous démontrons que l'aridité et les précipitations imprévisibles déterminent lesquels de ces taxons produisent une seule couvée. Les taxons qui vivent dans les milieux moins prévisibles produisent des oeufs plus gros relativement à leur taille que les taxons des milieux plus prévisibles. Homopus signatus produit les oeufs les plus gros, compte tenu de sa taille, probablement afin d'améliorer la survie des ses rejetons dans un environnement rude. La taille du corps, la dimension de l'ouverture pelvienne et l'étroitesse du passage anal semblent restreindre la taille des oeufs. Malgré ces contraintes, les femelles produisent des oeufs à coquille rigide plus grands que leur canal pelvien et utilisent la cinétique du pelvis pour faire passer les oeufs lors de la ponte. Ces caractéristi-ques sont inconnues chez les autres chéloniens, ce qui souligne l'avantage sélectif des gros oeufs chez H. signatus.[Traduit par la Rédaction] Hofmeyr et al. 1352

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Climate change models predict that the range of the world's smallest tortoise, Homopus signatus signatus, will aridify and contract in the next decades. To evaluate the eVects of annual variation in rainfall on the growth of H. s. signatus, we recorded annual growth rates of wild individuals from spring 2000 to spring 2004. Juveniles grew faster than did adults, and females grew faster than did males. Growth correlated strongly with the amount of rain that fell during the time just before and within the growth periods. Growth rates were lowest in 2002-2003, when almost no rain fell between September 2002 and August 2003. In this period, more than 54% of the tortoises had negative growth rates for their straight carapace length (SCL), shell height (SH), and shell volume (SV); maximum shrinking for SCL, SH, and SV was 4, 11, and 12%, respectively. The shell of H. s. signatus has some Xexibility dorso-ventrally, so a reduction in internal matter due to starvation or dehydration may have caused SH to shrink. Because the length and width of the shell seem more rigid, reversible bone resorption may have contributed to shrinkage, particularly of the shell width and plastron length. Based on growth rates for all years, female H. s. signatus need 11-12 years to mature, approximately twice as long as would be expected allometrically for such a small species. However, if aridiWcation lowers average growth rates to the level of 2002-2003, females would require 30 years to mature. Additionally, aridiWcation would lower average and maximum female size, resulting in smaller eggs and hatchlings. These projected life history responses to aridiWcation heighten the threat posed by the predicted range contraction of this red-listed species.

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Long‐lived, iteroparous species exhibit various mechanisms to overcome temporary unfavorable conditions and promote adult survival and population persistence. Consequently, populations may appear relatively stable while subtle and slow‐progressing threats cause their decline. The speckled tortoise (Homopus signatus) is a long‐lived, iteroparous species in South Africa that is thought to be secure in areas that meet the species’ known requirements. To verify its stability, I monitored a dense speckled tortoise population, integrating 2 mark‐recapture studies (2000–2004 and 2012–2015) in long‐term joint live and dead encounters and POPAN population models. From 2000 to 2015, the study site remained fenced, ungrazed, and was not modified in any way, yet the size‐class frequency distribution, sex ratio, and abundance of speckled tortoises drastically changed. Population numbers decreased 66%, mainly because of the disappearance of juveniles and males. Modeling results identified a reduction in the number of entrants into the population (via births and immigration) as the likely cause of population changes, whereas apparent survival remained high. Observations, in part anecdotal, of increasing numbers of pied crows (Corvus albus) on the study site suggest that increased predation on speckled tortoise hatchlings contributed to the population decline. Examination of rainfall data for 1990–2015 did not reveal evidence of aridification in the study area, a documented cause of reduced reproduction in speckled tortoises. The results of this study caution against the assumption that areas in the range of the speckled tortoise that meet its known requirements can maintain healthy populations. © 2017 The Wildlife Society