Reproductive Traits of Dusky Rattlesnakes (Crotalus Triseriatus)

Reproductive Traits of Dusky Rattlesnakes (Crotalus triseriatus) in Central Mexico Author(s): Hibraim Adán Pérez-Mendoza, Salomón Rubén Sanabria-Tobón, José Luis Jaramillo-Alba, Israel Solano-Zavaleta, Luis Felipe Vázquez-Vega, and Aníbal Helios Díaz de la Vega-Pérez Source: Journal of Herpetology, 52(1):6-11. Published By: The Society for the Study of Amphibians and Reptiles https://doi.org/10.1670/16-003 URL: http://www.bioone.org/doi/full/10.1670/16-003

BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder.

BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Journal of Herpetology, Vol. 52, No. 1, 6–11, 2018 Copyright 2018 Society for the Study of Amphibians and Reptiles

Reproductive Traits of Dusky Rattlesnakes (Crotalus triseriatus) in Central Mexico

1,2 1 1 HIBRAIM ADA´ N PE´ REZ-MENDOZA, SALOMOŃ RUBE´ N SANABRIA-TOBOŃ, JOSE´ LUIS JARAMILLO-ALBA, 3 3 4 ISRAEL SOLANO-ZAVALETA, LUIS FELIPE VA´ ZQUEZ-VEGA, AND ANI´BAL HELIOS DIÁZ DE LA VEGA-PE´ REZ

1Modulo de Ecologıá y Conservacioń, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autońoma de Me´xico, Avenida de los Barrios 1, Los Reyes Iztacala 54090, Tlalnepantla, Estado de Me´xico, Me´xico 3Departamento de Biologıá Evolutiva, Facultad de Ciencias, Universidad Nacional Autońoma de Me´xico, Ciudad Universitaria 04510, Distrito Federal, Me´xico 4Consejo Nacional de Ciencia y Tecnologıá-Centro Tlaxcala de Biologıá de la Conducta, Universidad Autońoma de Tlaxcala. Carretera Tlaxcala-Puebla km 1.5, C.P. 90062, Tlaxcala, Me´xico

ABSTRACT.—Reproductive aspects of most snake species remain elusive because of secretive habits or rarity. Here, we report data on litters of Crotalus triseriatus from two populations in central Mexico. We made 4-d visits to both study sites every other week from April to June during 2014 and 2015 (Site 1) and during 2015 (Site 2). Surveys were made from 0900 to 1800 h to catch as many gravid females as possible. All adult females were maintained in captivity until parturition. We recorded a total of 16 litters (10 from Site 1 and six from Site 2). Average litter size was 7.2 6 2.2 (n = 13), higher than previously reported in the species. We found no relationship between maternal snout–vent length (SVL) and litter size, and litter size did not differ between study sites or years. In contrast with other studies, we found no relationship between neonate SVL, body mass, and litter size or between maternal and neonatal traits. Dusky Rattlesnakes demonstrate a plastic reproductive response to changing environmental conditions. Neonate body size varied between sites, indicating that local selection may act through predation pressure, prey availability, or other environmental variables. Local selection may lead to differences in life history traits, whereas annual variation in factors such as prey availability might inﬂuence reproductive traits. Our study highlights the need for long-term studies to understand the sources of variation in life history.

RESUMEN.—Los atributos reproductivos de la mayorıá de las especies de serpientes permanecen desconocidos debido a sus ha´bitos sigilosos o a su rareza. En este estudio reportamos datos sobre camadas de Crotalus triseriatus de dos poblaciones del centro de Me´xico. Hicimos visitas de cuatro dıás a ambos sitios de estudio cada dos semanas desde abril a junio en 2014 y 2015 (Sitio 1) y en 2015 (Sitio 2). La bu´squeda se realizo´de 0900 a 1800 h para capturar tantas hembras gra´vidas como fuera posible. Todas las hembras adultas se mantuvieron en cautiverio hasta el parto. Registramos un total de 16 camadas (10 del Sitio 1 y seis del Sitio 2). El taman˜ o promedio de camada fue de 7.2 6 2.2 (n=13), mayor que el que se habıá reportado anteriormente. No existe una relacioń entre la longitud hocico-cloaca (LHC) de la madre y el taman˜ o de camada. No existieron diferencias significativas en el taman˜ o de camada entre los sitios de estudio y entre an˜ os de estudio. En contraste con otros estudios, no encontramos relacioń entre la longitud hocico-cloaca de los neonatos, la masa corporal y el taman˜ o de camada o relaciones entre los atributos de los neonatos y los atributos maternos. Crotalus triseriatus muestra una respuesta pla´stica en su reproduccioń a los cambios en las condiciones ambientales. La talla de los neonatos varioéntre sitios, indicando que las fuerzas selectivas locales pueden actuar a trave´s de las presiones de depredacioń, disponibilidad de presas u otras variables ambientales. La seleccioń local puede llevar a diferencias en los atributos de historia de vida, mientras que la variacioń anual en los factores ambientales como la disponibilidad de presas puede influir sobre los atributos reproductivos. Nuestro estudio resalta la necesidad de estudios a largo plazo para entender las fuentes de variacioń sobre los atributos de historia de vida.

Reproduction is considered an important life history trait as necessary to obtain robust information through studies specif- one of the main components of individual fitness (Stearns, 1992; ically designed to obtain these data. Also, litter size and Roff, 2002). However, for many species this trait is still reproductive effort can vary widely in different environments unknown or poorly understood in many secretive or rare taxa, because of local adaptation (Jenkins et al., 2009). Therefore, including most snakes. Some groups have received more understanding life history traits associated with reproduction in attention from researchers, due to their abundance and ease of snakes will require studies specifically designed to elucidate capture because of den or hibernacula aggregation; e.g., spatial and temporal variation and also particular relationships, Thamnophis sirtalis, Thamnophis elegans, and Thamnophis radix such as those between litter size and female body metrics. (Rossman et al., 1996; Sparkman et al., 2007; Miller et al., 2011); Reproduction is costly and therefore is constrained by energy Natrix tesselata (Sukalo et al., 2014); Vipera aspis, Vipera berus, and availability (Shine and Schwarzkopf, 1992; Lourdais et al., 2002). Vipera ursinii (Bonnet et al., 2000, 2003; Madsen et al., 2000; Dichotomous strategies identified in vertebrate reproduction are U´jva´ri et al., 2000); and Crotalus oreganus (Jenkins et al., 2009). income breeding (energy acquired during vitellogenesis) and However, there are many poorly known Crotalus species, capital breeding (energy acquired before vitellogenesis). Costs despite the fact that some are locally abundant (Setser et al., of reproduction are more evident for capital breeders, as stored 2010). Gathering information about reproduction is crucial for energy and expenditure can be measured before and after a conservation strategies (Prival and Schroff, 2012). reproductive event (Doughty and Shine, 1997). Like most Key information on reproduction, such as clutch or litter viviparous snakes, rattlesnakes are known to stop feeding sizes, is often restricted to short notes describing one or two when gravid (Gregory et al., 1999; Gregory, 2001; Webber et al., clutches or litters obtained incidentally; however, to understand 2012), and this could generate emaciation in postpartum the evolutionary forces driving reproductive traits, it is females and contribute to many species having biennial or longer reproduction cycles (Blem, 1982; Brown, 1991; Schuett et 2Corresponding Author. E-mail: [email protected] al., 2011). Some species have been reported to produce litters DOI: 10.1670/16-003 yearly during high resource years (Setser et al., 2010; Schuett et REPRODUCTIVE TRAITS OF CROTALUS TRISERIATUS 7 al., 2011; Strugariu et al., 2014). Methods to follow populations (Arbutus xalapensis and Alnus jorullensis). At higher altitudes therefore may require several years to describe reproductive vegetation changes to mixed pine forest, grasslands (including frequency and trait variation in rattlesnakes. Bromus dolichocarpus, Stipa ichu, and Festuca amplissima), fir Dusky Rattlesnakes (Crotalus triseriatus) is a poorly known forest (Abies religiosa), and subalpine grasslands. Throughout the species native to west-central Mexico, which inhabits in entire range, C. triseriatus can be found primarily in grasslands, subhumid montane habitats (Campbell and Lamar, 2004). pine forests, and oak forests. Climate is subhumid temperate Despite the fact that this species has been reported as locally with summer rainfall (Cww following Ko¨ppen climate classifi- abundant, there are only six known records of litter size for C. cation; Ko¨ppen, 1900). Mean annual temperature range from 6 triseriatus: one from western Mexico in Jalisco, two from central to 88C with temperatures reaching 188C during the warmest Mexico (Zempoala, State of Mexico; Armstrong and Murphy, month and -38C during the coldest month. Mean annual 1979), and three from Mexico City (Ramı´rez-Bautista et al., rainfall ranges from 800 to 1,000 mm (CONANP, 2013). 1995). However, the litter from Jalisco reported in Armstrong Sampling Methods.—We made 4-d visits to both study sites and Murphy (1979) corresponds with a recently described every other week from April to June during 2014 and 2015 (Site 1) species (Bryson et al., 2014). Litter size is a trait under strong and during 2015 (Site 2), making a total of 12 visits (48 d) for Site natural selection and therefore may change through time and 1 and 6 (24 d) in Site 2. We surveyed from 0900 to 1800 h, which space on populations from the same species (Seigel and Ford, concurs with this species’ activity period, following a visual 2001; Jenkins et al., 2009). In this study we provide information encounter protocol (McDiarmid et al., 2012). We determined the from a sample of litters of C. triseriatus obtained during 2014 sex of captured snakes by probing, then recorded these and 2015 from two natural protected areas in central Mexico, measurements in the field: snout–vent length (SVL), tail length Cumbres del Ajusco in Mexico City (Site 1), and La Malinche in (TL), and body mass (BM). Gravidity was assessed through the state of Tlaxcala (Site 2). palpation and direct observation of females that usually (but not always) were posteriorly enlarged. We kept all adult females in captivity near Site 1 in the Laboratory of Animal Ecology of the MATERIALS AND METHODS Sciences Faculty (National Autonomos University of Mexico) Study Species.—Dusky rattlesnakes are a small-sized rattle- with natural sunlight and at ambient temperatures of 18 to 24 8C snake species occurring on the Mexican highlands of the volcanic in individual enclosures of 40 · 25 · 20 cm. In the lab, belt. It is a widespread species and can be found from central barometric pressure, temperature, and relative humidity were Veracruz to Estado de Me´xico and Morelos (Bryson et al., 2014). registered by a portable weather meter Kestrel 3500 (Kestrel Adults commonly exceed 600 mm SVL; sexual dimorphism has Meters) every hour from 0900 to 1800 h. We supplied water and been reported and males tend to be larger than females food (live domestic mice) ad libitum until snake’s parturition (Campbell and Lamar, 2004). Dusky Rattlesnakes holds the (usually within 20 d). Mice were removed after 2 h if a snake highest-altitude record for a viper on the Americas reaching 4,573 showed no interest in eating. After parturition, neonates were m a.s.l. (the only species known inhabiting at higher altitudes is weighed and measured individually. We did not attempt to Glodyus himalayanus, reaching 4,800 m a.s.l.; Mani and Giddings, determine sex of neonates because that presented an injury risk. 1980); however, the species is more abundant at elevations of Relative Litter Mass.—To compare reproductive effort among 3,000 to 3,200 m (Armstrong and Murphy, 1979). Recently, four females, relative litter mass (RCM) was calculated. We used the species within the C. triseriatus group on the east portion of the most widely used estimator, which was calculated as: litter mass Mexican Volcanic Belt were described by Bryson et al. (2014). divided by postpartum maternal mass (Tinkle, 1969; Shine, 1980). Some specimens from Colima, Jalisco, and Estado de Me´xico Unlike other methods for relative litter mass estimation, output is were previously considered as C. triseriatus, but are now not restricted between 0 and 1, because litter mass can be higher considered as three distinct taxa: Crotalus armstrongi, Crotalus than postpartum maternal mass. For litter mass we included campbelli (for those individuals of Colima and Jalisco), and stillborns and unfertilized ova, as they also represent an energetic Crotalus tlaloci (for individuals of Southern Estado de Me´xico and expenditure. Although this method has been criticized because it Guerrero) (Bryson et al., 2014). can be biased because of low detection on gravid females with Study Sites.—Site 1 (Cumbres del Ajusco) surrounds Mexico low RCM (Bonnet et al., 2003; Taylor and Denardo, 2005) and City (19.228N, 99.288W, datum WGS84; Fig. 1); it is formed by the there are other methods to estimate RCM (e.g., ratio of clutch to extinct volcano Xitle. Dominant vegetation is evergreen forest total calories, Vitt and Congdon, 1978; ratio of the clutch mass to (mainly Pinus hartwegii and P. montezumae) changing with total maternal mass, Vitt and Price, 1982; Seigel and Fitch, 1984), altitude to fir forest (Abies religiosa). At this site C. triseriatus is we decided to use this approach because it is easily compared commonly found in open pine forest and grasslands (Festuca with other studies. We also implemented a linear model of litter amplissima, F. livida, F. hephaestophila, Muhlenbergia macroura,and mass against postparturient mass following Lourdais et al. (2002) M. quadridentata) at elevations ranging from 2,950 to 3,200 m. and Bonnet et al. (2003). Climate is subhumid temperate with summer rainfall (Cww Body Condition.—In order to assess body condition, we following Ko¨ppen climate classification; Ko¨ppen, 1900). Mean obtained the residual scores from a regression between log SVL annual temperature ranges from 5 to 128C with temperatures and log BM, following the method proposed by Nulleau and reaching 228C during the warmest month and -38Cduringthe Bonnet (1996). Although new methods for body condition have coldest month. Mean annual rainfall ranges from 200 to 1,800 been developed (Peig and Green, 2009), the method we choose mm (INEGI, 2004). allows data to be obtained easily, and used widely, which allows Site 2 (La Malinche) is an isolated extinct volcano located in for direct comparisons with the results of others (Schulte- central Mexico (19.248N, 97.998W, datum WGS84; Fig.1). Hostedde et al., 2005). Vegetation at lower altitudes consists of oak forest (Quercus Statistical Analysis.—We used generalized linear models crassifolia, Q. crassipes, Q. dysophylla), pine forest (P. hartwegii, P. (GLMs) to examine relationships between litter size and maternal leiophylla, P. montezumae, P. pseudostrobus), and small hardwoods SVL. Considering that our litter-size data were composed of 8H.A.PE´ REZ-MENDOZA ET AL.

FIG. 1. Geographic location of study sites. Hollow star indicates Site 1, Cumbres del Ajusco located at southwestern Mexico City. Solid star indicates Site 2, La Malinche on the south border between Tlaxcala and Puebla, Mexico. Datum WGS 84. counts (number of neonates), a negative binomial distribution some individuals took 2 mo for parturition (from Site 1). In all was used with a log link function. This approach was taken cases, parturitions happened after heavy rain or low-baromet- because Poisson distribution is too restrictive, predicting smaller ric-pressure systems, when humidity greatly increased in the variation than observed on data, resulting in a lack of control of laboratory. A total of 16 litters were recorded (10 from Site 1 and type-1 error (probability of false discoveries; Anders and Huber, 6 from Site 2). Average litter size from the recorded litters of 2010). To explore site effects on neonatal SVL, we used a t-test, as captive females was 7.2 6 2.2. We found no relationship SVL showed a normal distribution (W = 0.99, P = 0.67). Neonatal between SVL and litter size (Z = 0.52, df = 12, P = 0.60). At Site body condition was not normally distributed (W = 0.97, P = 0.01) 1, 10 litters were recorded, 5 from each year. In 2014, we only however, so we used a Wilcoxon’s test. Relationships between obtained three litters in captivity; however, we included two mean neonate body condition and maternal traitis (SVL, gravid additional litters found in the wild without mothers, and with maternal body condition, and RCM) were tested through evidence (e.g., fresh embryo sacs) that birth had occurred in the Spearman’s correlations with Bonferroni’s correction to control previous 24 h. In both cases, neonates were found basking near for multiple comparisons. All statistical analyses were conducted other neonates that we considered to be siblings, in accordance in R 3.2.3 (R Development Core Team, 2008). We present with the observations of neonate aggregations and the parental summary statistics as mean 6 standard deviation throughout. care of Crotalus species (Butler et al., 1995; Greene et al., 2002). We decided to include these individuals despite lacking their mothers’ data in order to make our neonate estimates more RESULTS robust; however, data from these litters were not included in Of the eight gravid females captured from Site 1, one was litter size analysis, because missing even one individual may observed to eat while gravid. This individual gave birth to four bias our estimates strongly, given the sample size. The average unfertilized eggs and two partially developed dead embryos. litter size for Site 1 was 6.1 6 2.3, which was lower than our None of the gravid females from Site 2 made any attempt to eat reported average litter size, considering litters recorded for both during captivity. Parturition in the laboratory occurred from 16 sites (Table 1). The largest litter consisted of nine neonates. The May to 29 May in 2014 and 19 April to 20 June in 2015 for Site 1 smallest litter consisted of three. At Site 2, six litters were snakes, but occurred from 15 May to 23 June 2015 for Site 2 recorded, ﬁve from individuals kept in captivity and an snakes. Most individuals give birth after 20 d in captivity, but additional litter found in the wild without the mother. For the REPRODUCTIVE TRAITS OF CROTALUS TRISERIATUS 9

TABLE 1. Reproductive maternal traits of Crotalus triseriatus in central Mexico. SVL = snout-vent length, PrPBM = pre-partum body mass, PoPBM = post-partum body mass, RCM = relative litter mass, TLM = total loss mass (including total litter mass and body ﬂuids), and LS = litter size. In parentheses following litter size value is the total number of unfertilized eggs, undeveloped eggs, and partially developed dead embryos. Mean values are presented as 6 SD. For litter size, those litters observed in the ﬁeld were excluded from the calculation.

Individual number Site and year SVL (mm) PrPBM (g) PoPBM (g) RCM TLM (g) LS 1 1/14 404.0 62.40 35.23 0.61 27.17 5 2 1/14 374.0 38.10 20.71 0.71 17.39 5 3 1/14 487.0 143.60 107.84 0.16 35.76 5 – 1/14 – – – – – 4 – 1/14 – – – – – 4 4 1/15 420.0 102.00 45.76 1.08 56.24 9 (1) 5 1/15 395.1 81.00 40.35 0.62 40.65 7 (2) 6 1/15 440.5 108.30 54.50 0.70 53.80 9 (1) 7 1/15 379.0 103.00 66.00 0.20 37.00 0 (6) 8 1/15 470.0 174.00 73.13 0.63 100.87 3 1 2/15 458.9 158.40 92.10 0.60 54.90 9 2 2/15 444.3 115.50 67.00 0.46 30.50 8 3 2/15 476.7 141.90 73.13 0.63 45.92 10 4 2/15 406.3 109.50 51.70 0.73 37.60 8 5 2/15 536.5 144.60 90.60 0.44 39.70 8 – 2/15 – – – – 47.37 8 (1) Mean 437.9 6 47.4 114.0 6 38.7 62.9 6 24.9 0.6 6 0.2 51.1 6 21.2 7.2 6 2.2

latter, we followed the same criteria we applied to previous DISCUSSION litters for which a mother was not found nearby. In this case, Anorexia when gravid is a common pattern for viviparous four individuals were found basking next to a bunchgrass; after snakes (Gregory et al., 1999; Lourdais et al., 2002), and concurs searching under the bunchgrass leaves, four additional neonates with our observations on C. triseriatus. The only rattlesnake and a partially developed dead embryo were recorded. The known to feed regularly while gravid (Crotalus atrox) inhabits a average litter size for Site 2 was 8.6 6 0.9, ranging from 8 to 10 highly stochastic and warm environment (Schuett et al., 2013). neonates produced. Average litter size for Site 2 was higher than However, anorexia may be facultative, depending mainly on the average litter size (including data from both sites, Table 1). prey availability and behavioral changes while gravid, like Mean litter size did not differ by site (Z = 1.56, df = 11, P = 0.12) basking habits (Gregory et al., 1999; Gregory, 2001; Lourdais et or by year (Z = 1.05, df = 11, P = 0.29). al., 2002). The occurrence of parturition after heavy rains or low- Relative Litter Mass.—Average litter mass was 35.76 6 12.78 g barometric-pressure systems has been reported in rattlesnakes and ranged from 15.80 g (excluding the litter of unfertilized eggs (Setser et al., 2010; Schuett et al. 2011), although the reasons and partially developed dead embryos and those found in the remain unknown. Parturition occurred from April to June, field without the mother) to 54.90 g, more than a threefold following the same pattern described in most Mexican live- difference. Average litter mass per site indicates that litter mass bearing species in the central Mexican highlands (Setser et al., was higher at Site 2 (41.72 6 9.19 g) than at Site 1 (31.49 6 13.86 2010; Pe´rez-Mendoza et al., 2014). Our results contrast with g). However, this difference was not statistically significant (W = reports from other rattlesnake species distributed at higher 9.5, df = 11, P = 0.07). Mean RCM was 0.63 6 0.22 (excluding the latitudes, which are more likely to give birth from August to same data explained above), and ranged from 0.19 to 1.08; October (Martin, 2002; Cardwell, 2008; Schuett et al., 2011). indicating that litter mass was higher than postpartum mass. It is However, differences on parturition timing among species may noteworthy that snakes can lose so much body mass during be associated with size at birth (as most of northern species are parturition. Average RCM was 0.67 6 0.28 at Site 1 and did not larger than those from Mexican highlands), where larger differ from that at Site 2 0.57 6 0.12 (W = 24.50, df = 11, P = neonates take longer to develop, or with seasonal variation in 0.56). We found no statistical difference between years at Site 1 prey abundance, which increases during May and June in with an average RCM of 0.49 6 0.29 for 2014 and a RCM of 0.65 central Mexico with the start of the wet season (pers. obs.). 6 0.31 for 2015. Females lost as much as 100.87 g and as little as Litter size at our study sites was similar to those previously 37.00 g, it is noteworthy that a large percentage of this loss in reported (Armstrong and Murphy, 1979; Ramı´rez-Bautista et al., body mass (4–64%) corresponds with body fluids and not to litter 1979); our results were also consistent with litter sizes reported mass. for other rattlesnake species (e.g., Crotalus horridus and Crotalus Neonate and Maternal Traits.—We measured 103 neonates, polystictus; Brown et al., 2007; Setser et al., 2010). Yet, they differ including 51 from Site 1 and 52 from Site 2. Neonates averaged: from other species with smaller litters (e.g., C. oreganus, Diller mass of 4.13 g 6 0.69, SVL of 145.74 mm 6 14.28, and TL of 16.46 and Wallace, 2002; Crotalus pricei, Prival and Schroff, 2012; and mm 6 1.23 (Table 2). Our results indicate that neonates from Site C. atrox, Taylor and Denardo, 2005; Schuett et al., 2011). These 2 were heavier and longer than neonates from Site 1. However, results suggest that fecundity may be associated more closely only the observed differences in body mass were statistically with local selection pressures than with phylogenetic con- significant (W = 796.5, df = 100, P < 0.01). There were no straints. However, for most rattlesnake species litter size it is still differences between sites in maternal SVL (W = 9, df =12, P = largely unknown and further research is needed to understand 0.13) or maternal body mass (W = 8, df = 12, P = 0.09). variation in this life history trait. Spearman correlations between neonate average body condition, We found no relationship between maternal SVL and litter and maternal body condition, body mass, or SVL showed no size, unlike such relationships reported in other reptile species, significant relationships. including rattlesnakes (Jenkins et al., 2009; Setser et al., 2010); 10 H. A. PE´ REZ-MENDOZA ET AL.

TABLE 2. Morphometrics of neonate Crotalus triseriatus in central Mexico. SVL = snout-vent length, TL = tail length, BM = body mass, and BC = body condition. Mean values are presented 6 SD.

Origin litter Site SVL TL BM BC 1 1 157.8 6 7.6 16.2 6 1.3 4.74 6 0.31 -0.03 6 0.48 2 1 120.8 6 5.1 15.4 6 1.1 3.16 6 0.21 0.03 6 0.19 3 1 144.4 6 17.2 16.0 6 1.6 4.04 6 1.51 -0.12 6 0.73 – 1 167.5 6 7.8 14.5 6 0.7 4.90 6 0.28 -0.34 6 0.10 – 1 147.0 6 4.3 16.0 6 4.6 3.95 6 0.39 -0.31 6 0.58 4 1 162.6 6 12.3 19.2 6 3.7 4.38 6 0.58 -0.63 6 0.31 5 1 131.4 6 9.9 15.9 6 2.7 3.42 6 0.61 -0.16 6 0.50 6 1 137.4 6 9.8 17.1 6 1.9 3.69 6 0.47 -0.15 6 0.43 8 1 133.8 6 2.7 16.3 6 2.4 3.39 6 0.24 -0.28 6 0.12 1 2 159.0 6 3.7 17.8 6 2.2 4.92 6 0.22 -0.10 6 0.29 2 2 131.8 6 5.2 14.7 6 1.6 3.23 6 0.58 -0.36 6 0.47 3 2 129.6 6 5.6 15.8 6 1.1 3.62 6 0.31 0.13 6 0.30 4 2 159.1 6 4.1 17.6 6 2.7 4.53 6 0.23 -0.30 6 0.26 5 2 148.9 6 4.4 16.8 6 1.9 4.70 6 0.34 0.36 6 0.29 – 2 155.1 6 3.6 17.4 6 2.0 5.26 6 0.28 0.63 6 0.37 Mean 145.5 6 15.2 16.7 6 2.4 4.15 6 0.83 -0.06 6 0.49

this may be because of a genuine lack of such a relationship Ramos, and D. I. Aragon-Barragan for their assistance in the (Taylor and Denardo, 2005), or because our small sample sizes field. We also thank M. Martıńez-Go´mez and J. Va´zquez-Pe´rez were insufficient to evaluate this relationship. However, this for their valuable help with logistics and use of the field station pattern may be obscured by interannual variation on litter size. at La Malinche facilities to conduct part of our field work. Relative Litter Mass.—Average RCM was high (0.63) in this Finally, S. Ruiz and two anonymous reviewers provided helpful species, apparently the second highest recorded for a viviparous comments on this manuscript. This research was conducted terrestrial species (Shine, 1992; Seigel and Ford, 2001), with the with funds provided by UNAM, PAPIIT project number IA highest 0.70 reported for Crotalus polystictus (Setser et al., 2010). 204416. This trend may be associated with high prey abundance and low predator pressures (Li-xin et al., 2002; Shine, 2003). However, a study of prey abundance must be conducted to measure the local selective environment that could influence female body condition LITERATURE CITED and RCM. ANDERS, S., AND W. HUBER. 2010. Differential expression analysis for Neonate Traits.—Neonates from Site 2 were heavier than sequence count data. Genome Biology 11:R106. ARMSTRONG, B. L., AND J. B. MURPHY. 1979. The Natural History of neonates from Site 1; however, the differences were independent Mexican Rattlesnakes. University of Kansas, Museum of Natural of maternal characteristics. Size divergence might reflect a more History, USA. demanding environment from neonates at Site 2, where we BLEM, C. R. 1982. Biennial reproduction in snakes: an alternative observed that small prey were more scarce than at Site 1 (pers. hypothesis. Copeia 1982:961–963. BONNET, X., G. NAULLEAU,R.SHINE, AND O. LOURDAIS. 2000. Reproductive obs.). We suggest that increased selection on neonate capacity to versus ecological advantages to larger body sizes in female snakes, withstand prey scarcity may occur. Another plausible explana- Vipera aspis. Oikos 89:509–518. tion is that prey size at Site 2 may select for larger neonates (e.g., BONNET, X., R. SHINE,O.LOURDAIS, AND G. NAULLEAU. 2003. Measures of Shine, 2003), although this effect seems unlikely, as the main prey reproductive allometry are sensitive to sampling bias. Functional items (Sceloporus aeneus) at Site 2 are smaller than those at Site 1 Ecology 17:39–49. BROWN, W. S. 1991. Female reproductive ecology in a northern (Sceloporus grammicus and Sceloporus torquatus). All other neonate population of the timber rattlesnake, Crotalus horridus. Herpetologica traits did not differ between sites. However, the measured traits 47:101–115. varied widely, indicating that there may be not a ‘‘better’’ strategy BROWN, W. S., M. KE´ RY, AND J. E. HINES. 2007. Survival of timber for neonate size, or that increased variance in this trait is favored rattlesnakes (Crotalus horridus) estimated by capture–recapture models in relation to age, sex, color morph, time, and birthplace. (probably as a bet-hedging strategy). Another possible explana- Copeia 2007:656–671. tion is that neonate size is strongly affected by tradeoffs between BRYSON, R. W., C. W. LINKEM,M.E.DORCAS,A.LATHROP,J.M.JONES,J. litter size and offspring size, a commonly observed inverse ALVARADO-DIÁZ,C.I.GRU¨ NWALD, AND R. W. MURPHY. 2014. Multilocus relationship in snakes (Seigel and Ford, 1987). species delimitation in the Crotalus triseriatus group (Serpentes: Selection on local populations may lead to differences in life Viperidae: Crotalinae), with description of two new species. Zootaxa 3826:475–496. history traits, as we found for litter size and neonate body mass. BUTLER, J. A., T. W. HULL, AND R. FRANZ. 1995. Neonate aggregations and However, annual variation suggests that litter size may respond maternal attendance of young in Eastern Diamondback Rattlesnake, quickly to factors such as prey availability, as previously Crotalus adamanteus. Copeia 1995:196–198. observed in Thamnophis marcianus (Ford and Seigel, 1989). We CAMPBELL, J. A., AND W. W. LAMAR. 2004. The Venomous Reptiles of the Western Hemisphere. Cornell University Press, USA. question the relative importance of local adaptation versus CARDWELL, M. D. 2008. The reproductive ecology of Mohave rattle- temporal plasticity in this trait. We favor long-term studies to snakes. Journal of Zoology 274:65–76. understand the sources of variation and their relative impor- CONANP. 2013. Programa de Manejo Parque Nacional La Montanã tance for reproductive trait evolution better. Malinche o Matralcueýatl. Secretarıá de Medio Ambiente y Recursos Naturales, Me´xico. DILLER,L.V.,AND R. L. WALLACE. 2002. Growth, reproduction, and Acknowledgments.—We would like to thank S. J. Gonza´lez- survival in a population of Crotalus viridis oreganus in north central Ramos, C. U. Reyes-Medina, J. L. Mohzo-Casillas, E. Salas- Idaho. Herpetological Monographs 16:26–45. REPRODUCTIVE TRAITS OF CROTALUS TRISERIATUS 11

DOUGHTY,P.,AND R. SHINE. 1997. Detecting life history trade-offs: ROFF, D. A. 2002. Life History Evolution. Sinauer Associates Inc., USA. measuring energy stores in ‘‘capital’’ breeders reveals costs of ROSSMAN, D. A., N. B. FORD, AND R. A. SIEGEL. 1996. The Garter Snakes: reproduction. Oecologia 110:508–513. Evolution and Ecology. University of Oklahoma Press, USA. FORD, N. B., AND R. A. SEIGEL. 1989. Phenotypic plasticity in reproductive SCHUETT, G. W., R. A. REPP, AND S. K. HOSS. 2011. Frequency of traits: evidence from a viviparous snake. Ecology 70:1768–1774. reproduction in female Western Diamond-backed Rattlesnakes GREENE, H. W., P. G. MAY,D.L.HARDY,J.M.SCITURRO, AND T. M. FARREL. from the Sonoran Desert of Arizona is variable in individuals: 2002. Parental behavior by vipers. Pp. 179–205 in G. W. Schuett, M. potential role of rainfall and prey densities. Journal of Zoology 284: Hoggren, M. E. Douglas, and H. W. Greene (eds.), Biology of the 105–113. Vipers. Eagle Mountain Publishing, USA. SCHUETT, G.W., R. A. REPP,M.AMARELLO, AND C. F. SMITH. 2013. Unlike GREGORY, P. T. 2001. Feeding, thermoregulation, and offspring viability in most vipers, female rattlesnakes (Crotalus atrox) continue to hunt and gravid garter snakes (Thamnophis sirtalis): what makes laboratory feed throughout pregnancy. Journal of Zoology 289:101–110. results believable? Copeia 2001:365–371. SCHULTE-HOSTEDDE, A. I., B. ZINNER,J.S.MILLAR, AND G. J. HICKLING. 2005. GREGORY, P. T., L. H. CRAMPTON, AND K. M. SKEBO. 1999. Conflicts and Restitution of mass-size residuals: validating body condition indices. interactions among reproduction, thermoregulation and feeding in Ecology 86:155–163. viviparous reptiles: are gravid snakes anorexic? Journal of Zoology SEIGEL, R. A., AND H. S. FITCH. 1984. Ecological patterns of relative clutch 248:231–241. mass in snakes. Oecologia 61:293–301. INEGI. 2004. Carta de clima. 1:250000, code E14A49. INEGI, Mexico. SEIGEL, R. A., AND N. B. FORD. 1987. Reproductive ecology. Pp. 210–252 in JENKINS, C. L., C. R. PETERSON,S.C.DOERING, AND V. A. COBB. 2009. R. A. Seigel, J. T. Collins, and S. S. Novak (eds.), Snakes: Ecology and Microgeographic variation in reproductive characteristics among Evolutionary Biology. McGraw Hill Publishing Company, USA. western rattlesnake (Crotalus oreganus) populations. Copeia 2009: SEIGEL, R. A., AND N. B. FORD. 2001. Phenotypic plasticity in reproductive 774–780. traits: geographical variation in plasticity in a viviparous snake. KO¨ PPEN, W. 1900. Versuch einer Klassifikation der Klimate, vorzugsweise Functional Ecology 15:36–42. nach ihren Beziehungen zur Pflanzenwelt. Geographische Zeitschrift ˜ 6:593–611, 657–679. SETSER, K., E. MOCINO-DELOYA,J.M.PLEGUEZUELOS,D.LAZCANO, AND A. KARDON. 2010. Reproductive ecology of female Mexican Lance- LI-XIN, S., R. SHINE,Z.DEBI, AND T. ZHENGREN. 2002. Low costs, high output: reproduction in an insular pit-viper (Gloydius shedaonensis, headed Rattlesnakes. Journal of Zoology 281:175–182. Viperidae) from north-eastern China. Journal of Zoology 256:511– SHINE, R. 1980. ‘‘Costs’’ of reproduction in reptiles. Oecologia 46:92–100. 521. SHINE, R. 1992. Relative clutch mass and body shape in lizards and LOURDAIS, O., X. BONNET, AND P. D OUGHTY. 2002. Costs of anorexia during snakes: is reproductive investment constrained or optimized? pregnancy in a viviparous snake (Vipera aspis). Journal of Experi- Evolution 46:828–833. mental Zoology 292:487–493. SHINE, R. 2003. Reproductive strategies in snakes. Proceedings of the MADSEN, T., M. OLSSON,H.WITTZELL,B.STILLE,A.GULLBERG,R.SHINE,S. Royal Society of London Series B—Biological Sciences 270:995–1004. ANDERSSON, AND H. TEGELSTO¨ RM. 2000. Population size and genetic SHINE, R., AND L. SCHWARZKOPF. 1992. The evolution of reproductive effort diversity in sand lizards (Lacerta agilis) and adders (Vipera berus). in lizards and snakes. Evolution 46:62–75. Biological Conservation 94:257–262. SPARKMAN, A. M., S. J. ARNOLD, AND A.M. BRONIKOWSKI. 2007. An empirical MANI, M., AND L. GIDDINGS. 1980. Ecology of highlands (Vol. 40). Dr. W. test for reproductive senescence and reproductive effort in the garter Junk b.v. Publishers, Netherlands. snake Thamnophis elegans. Proceedings of the Royal Society of MARTIN, W. H. 2002. Life history constraints on the timber rattlesnake London Series B—Biological Sciences 274:943–950. (Crotalus horridus) at its climatic limits. Pp. 285–306 in G. W. Schuett, STEARNS, S. C. 1992. The Evolution of Life Histories. Oxford University M. Hoggren, and M. E. Douglas (eds.), Biology of Vipers. Eagle Press, UK. Mountain Publishing, USA. STRUGARIU,A.,I.GHERGHEL, AND S.R.ZAMFIRESCU. 2014. Annual MCDIARMID, R. W., M. S. FOSTER,C.GUYER, AND W. GIBBONS. 2012. Reptile reproduction in female adders (Vipera berus) from a montane Biodiversity: Standard Methods for Inventory and Monitoring. environment. Journal of Herpetology 48:552–555. University of California Press, USA. SUKALO, G., S. DORDEVIC´,S.GVOZDENOVIC´,A.SIMOVIC´,M.ANDELOKOVIC´,V. MILLER, D. A., W. R. CLARK,S.J.ARNOLD, AND A. M. BRONIKOWSKI. 2011. BLAGOJEVIC´, AND L. TOMOVIC´. 2011. Intra- and inter-population Stochastic population dynamics in populations of western terrestrial variability of food preferences of two Natrix species on the Balkan garter snakes with divergent life histories. Ecology 98:1658–1671. Peninsula. Herpetological Conservation and Biology 9:123–136. NULLEAU, G., AND X. BONNET. 1996. Body condition threshold for breeding TAYLOR, E. N., AND D. F. DENARDO. 2005. Reproductive ecology of Western in a viviparous snake. Oecologia 107:301–306. Diamond-Backed Rattlesnakes. Copeia 2005:152–158. PEIG, J., AND A. J. GREEN. 2009. New perspectives for estimating body TINKLE, D. W. 1969. The concept of reproductive effort and its relation to condition from mass/length data: the scale mass index as an the evolution of life histories of lizards. The American Naturalist 203: alternative method. Oikos 118:1883–1891. 501–516. E´ REZ ENDOZA U´ N˜ IGA EGA ARTORELL URITA P -M , H. A., J. J. Z -V ,C.M ,Y.H.Z - U´JVA´ RI, B., Z. KORSO´ S, AND T. PE´ CHY. 2000. Life history, population GUTIE´ RREZ,I.SOLANO-ZAVALETA,A.L.HERNA´ NDEZ-ROSAS, AND A. characteristics and conservation of the Hungarian meadow viper MOLINA-MOCTEZUMA. 2014. Patterns of spatio-temporal variation in (Vipera ursinii rakosiensis). Amphibia–Reptilia 21:267–278. the survival rates of a viviparous lizard: the interacting effects of sex, VITT, L. J., AND J. D. CONGDON. 1978. Body shape, reproductive effort, and reproductive trade-offs, aridity, and human-induced disturbance. relative clutch mass in lizards: resolution of a paradox. The Population Ecology 56:605–618. American Naturalist 112:595–608. PRIVAL, D. B., AND M. J. SCHROFF. 2012. A 13-year study of a northern VITT,L.J.,AND H. J. PRICE. 1982. Ecological and evolutionary population of twin- spotted rattlesnakes (Crotalus pricei): growth, determinants of relative clutch mass in lizards. Herpetologica 38: reproduction, survival, and conservation. Herpetological Mono- 237–255. graphs 26:1–18. WEBBER, M. M., X. GLAUDAS, AND J.A. RODRI´GUEZ-ROBLES. 2012. Do RDEVELOPMENT CORE TEAM. 2008. R: a language and environment for statistical computing. R Foundation for Statistical Computing. sidewinder rattlesnakes (Crotalus cerastes, Viperidae) cease feeding Vienna, Austria. http://www.R-project.org. during the breeding season? Copeia 2012:100–105. RAMI´REZ-BAUTISTA, A., G. GUTIE´ RREZ-MAYE´ N, AND A. GONZA´ LEZ-ROMERO. 1995. Clutch sizes in a community of snakes from the mountains of Accepted: 12 July 2017. the Valley of Mexico. Herpetological Review 26:12–13. Published online: 25 January 2018.