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Danaus erippus, sister species of the monarch butterfly D.plexippus. Picture courtesy of Myrian Medina..
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... Previous research indicates resident populations in south Florida occur year-round [e.g., 21,[25][26][27][28], but the degree of connectivity with the migratory population has not been examined. The use of cardenolide fingerprinting has revealed that southern Florida populations receive northern-origin migratory monarchs during the autumn that break diapause and begin breeding [21]. ...
Alternative life history strategies are mechanisms by which organisms are able to maximize fitness across a range of environmental conditions. Fitness is maximized by different strategies depending on context, resulting in trade-offs between life history strategies. Monarch butterflies (Danaus plexippus) employ both migratory and resident life history strategies. Since residents breed throughout the year, but migrants overwinter in reproductive diapause, there are fitness trade-offs between the two strategies. We used stable isotope analysis to evaluate the geographic origins of monarchs in a yearround population in south Florida. Based on stable isotope profiles of hydrogen and carbon (δ ² H and δ ¹³ C values), we found that 48% (16/33) of monarchs collected in south Florida are migrants that originated from outside the sampling region. Migrants had a larger wing length than residents; thus, switching to a resident strategy could alter their probability of reproductive success. Further work is needed to investigate the mechanism underlying this pattern, but these findings show that alternate life history strategies and sex-specific behaviors are underexplored factors influencing monarch migration and evolution.
... In Cuba, migrants arrive in November from south-eastern Canada and the south-eastern USA. Initial results (Dockx, 2002(Dockx, , 2007Dockx et al., 2004) show that Cuban monarchs do not overwinter and do not remigrate to the USA. The present study is the first attempt to review, consolidate, and interpret the existing data of migrant monarchs that follow a more eastern migratory route through Florida-Cuba; this unified version is intended to offer a framework for the interpretation of future data and to pinpoint future monarch research areas. ...
... The third line of evidence that this hybridization is taking place comes from similar wing colorations and wing sizes between Cuban resident monarchs (suspected hybrids) collected in November ( Fig. 10 and Table 4) and hybrids obtained in the laboratory from two controlled crosses of D. p. megalippe ¥ D. p. plexippus (Figs 11,12 and Table 5). Detailed information about these crosses is provided by Dockx (2002). It is suspected that this hybridization of D. p. plexippus with the local monarch subspecies is repeated in other areas of insular and continental Caribbean. ...
... Males (N = 3; mean ± SD = 5.17 ± 0.16 cm) of D.p. plexippus were collected in Minnesota, USA (nonspecific location available) in early September and females breeders (N = 5; mean ± SD = 4.4 ± 0.093 cm) of D. p. megalippe were collected in August in Cerritos-Risaralda, South America (4°80′N, 75°83′W). For a complete description of this hybrid cross, see Dockx (2002). ...
The eastern North American population of the monarch butterfly (Danaus plexippus plexippus) has different migratory routes. The majority fly to overwintering colonies in Mexico and others take an eastern route through Florida and Cuba. Monarchs migrating through Florida–Cuba do not overwinter and are mostly found nectaring and flying close to vegetation. This present study explores whether Florida–Cuba versus Mexican migrants differ in (1) phenotypic traits important for migration (e.g. wing size and condition, lipid and lean mass content, and reproductive status) and (2) migratory strategies. The monarch natal grounds (e.g. migrants versus residents) were determined through thin-layer chromatography cardenolide fingerprint and stable isotopes (hydrogen d 2 H and carbon d 13 C). In addition, wing size and condition, lipid and lean mass, and reproductive status were determined. The results suggest that Mexican migrants are better suited for longer sustained flights and successful overwinter periods as a result of larger wings in better condition, reproductive diapause, and signifi-cant fat content. By contrast, Florida–Cuba migrants are more suited for shorter flights and opportunistic migratory strategies, given that their wings were in poor condition, as well as the active reproductive status of > 50% of these butterflies and their significantly low fat content. Eastern monarch migration is more complex and diverse than previously assumed.
... Our result was consistent with many (e.g. Beall 1946; Herman 1988; Calvert & Lawton 1993; Van Hook 1993 Knight 1998; Oberhauser & Frey 1999; Borland et al. 2004; Dockx 2002 Dockx , 2007 Brindza et al. 2008; Altizer & Davis 2010) but not all (e.g. Tuskes & Brower 1978; James 1984; Frey et al. 1998; Leong et al. 1993; Knight 1998; Malcolm et al. 1989; Dockx 2002 Dockx , 2007) findings based on various monarch populations. ...
... Beall 1946; Herman 1988; Calvert & Lawton 1993; Van Hook 1993 Knight 1998; Oberhauser & Frey 1999; Borland et al. 2004; Dockx 2002 Dockx , 2007 Brindza et al. 2008; Altizer & Davis 2010) but not all (e.g. Tuskes & Brower 1978; James 1984; Frey et al. 1998; Leong et al. 1993; Knight 1998; Malcolm et al. 1989; Dockx 2002 Dockx , 2007) findings based on various monarch populations. Although our literature review showed that the sexes are usually considered separately (Table 1), this was not always the case (e.g. ...
Standardized measurements using well-defined landmarks are the most effective means to reduce measurement error. We describe such a protocol for monarch forewings based on single measurements with a ruler to the nearest 1.0 mm. Analysis of this protocol showed that it provides excellent intra-observer repeatability, excellent to substantial inter-observer repeatability, and similar wing length estimates as those of calipers at 0.1 mm, as long as sample sizes are > 30. In addition, our study showed that males and females differ in wing length; different observers differ in their measurements and in their measurement error; and wings shrink slightly when dried. We make these recommendations for study of monarch wing lengths: 1) males and females should be analyzed separately; 2) live butterflies should be measured after cooling and dead butterflies should be measured before they are dried; 3) measurements should be restricted to the right forewing; 4) the standard protocol should be practiced and calibrated until measurements are repeatable within and among measurers; 5) the samples should be mixed among all observers when possible to mitigate relative biases; and 6) names, handedness, measurement error, and archived raw data should be reported. Widespread adoption of this protocol will increase the comparability of wing length data from various investigators. Similarly based standardization of measurement would benefit wing measurement of all Lepidoptera.
... Some move eastward, toward the Atlantic coast of the USA (Urquhart, 1987) and south, arriving in southern Florida (Knight, 1998) and Cuba (Dockx et al., 2004). Comparisons of reproductive stage, lipid content and wing condition between Mexican (Alonso, 1996), south Florida (Knight, 1998) and Cuban (Dockx, 2002) migrant monarchs show that Florida and Cuban monarchs are part of the same migrant group that fly through this southern peninsula to the Caribbean. The existence of two different migratory routes for eastern North American monarchs, Mexico and Florida-Cuba, is supported as well by the differences in the natal grounds of Mexican and Cuban monarchs. ...
... Instead, some of them mix with the resident Cuban population, and others continue to other areas of the insular and continental Caribbean (Dockx et al., 2004). Support for the mixing of these groups of monarchs came from the active reproductive status of the migrant monarchs, observations of migrants checking plants to oviposit, and the intermediate phenotypes of these two subspecies when migrants are present on the island (Dockx, 2002). When migrant monarchs arrive at Cuba, they encounter a permanent resident monarch population, Danaus plexippus megalippe (Hübner) (Fig. 2) that does not migrate, and breeds all year round. ...
... Fourteen other mounted monarchs collected by Hernandez in Guanahacabibes in November 1993 were also included in this work. A complete description of localities, dates, the number of individuals collected and collection methods can be found in Dockx (2002). ...
The majority of migrant monarchs (Danaus plexippus) from the eastern USA and south-eastern Canada migrate to Mexico; however, some of them migrate to Cuba. Cuban migrants hatch in south-east Canada and eastern USA, and then engage in a southern trip of 4000 km to this Caribbean island. In Cuba, these migrants encounter resident monarchs, which do not migrate, and instead move between plant patches looking for nectar, mating partners and host plants. These differences in flight behaviour between migrant and resident Cuban monarchs may have resulted in different selective pressures in the wing size and shape. Two modes of selection were tested, directional and stabilizing. In addition, wing condition was compared between these two groups. Monarchs were collected for 4 years in Cuba and classified as resident or migrant using two independent techniques: Thin-layer chromatography and stable hydrogen and stable carbon isotope measurements. Wing size was measured and wing condition was rated in the butterflies. Fourier analysis and wing angular measurements were used to assess wing shape differences. Migrants have significantly longer wings than residents, thus supporting the action of directional selection on wing size. In addition, directional selection acts on wing shape; that is, migrant females differ significantly from resident females in their wing angles. However, the results do not support the action of stabilizing selection: there was no significant variance between migrant and resident monarchs in their wing size or shape. Also, migrant females and males differed in wing condition as a result of differences in flight behaviour. In conclusion, eastern North American monarchs offer a good opportunity to study the selective pressures of migration on wing morphology and how different migratory routes and behaviours are linked to wing morphology and condition. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 605–616.
... The numbers of migrants generally outnumbered residents and many (ϳ90%) of these individuals were reproductively active (Dockx 2002), suggesting gene flow into the Caribbean D. p. megalippe population from D. p. plexippus (Appendix). We suspect that this same movement from the North American continent and gene flow may also occur on other Caribbean islands and perhaps on the Yucatan peninsula. ...
Since the discovery of monarch butterfly (Danaus plexippus) overwintering colonies in Mexico in the 1970s, it was assumed that monarchs from eastern North America migrated only to Mexico. This paper reveals that monarchs from Canada and the east coast of the United States also regularly travel to Cuba during the migration period. The natal grounds of Cuban monarchs were determined through the combined use of stable hydrogen (D) and stable carbon (13 C) isotope measurements and by cardenolide fingerprint analysis using thin-layer chromatography (TLC). The TLC data revealed that there was an influx of migrants in November to Cuba, and the stable isotope data revealed that migrant Cuban monarchs originated from southeastern Canada and the eastern United States. Our findings suggest that North American migrant monarchs that move to Cuba hybridize with resident populations there and do not return to the continent. The differences in the natal grounds, migratory route, and reproductive stages between monarchs wintering in Mexico and Cuba suggest that there are at least two subpopulations of eastern North American monarchs. The extent to which Cuba may act as a bridge for monarch movement to the Yucatan and other Caribbean islands and the genetic impact of this newly revealed flux in monarch movements remain to be determined.
The demands of long-distance flight represent an important evolutionary force operating on the traits of migratory species. Monarchs are widespread butterflies known for their annual migrations in North America. We examined divergence in wing morphology among migratory monarchs from eastern and western N. America, and nonmigratory monarchs in S. Florida, Puerto Rico, Costa Rica, and Hawaii. For the three N. American populations, we also examined monarchs reared in four common environment experiments. We used image analysis to measure multiple traits including forewing area and aspect ratio; for laboratory-reared monarchs we also quantified body area and wing loading. Results showed wild monarchs from all nonmigratory populations were smaller than those from migratory populations. Wild and captive-reared eastern monarchs had the largest and most elongated forewings, whereas monarchs from Puerto Rico and Costa Rica had the smallest and roundest forewings. Eastern monarchs also had the largest bodies and high measures of wing loading, whereas western and S. Florida monarchs had less elongated forewings and smaller bodies. Among captive-reared butterflies, family-level effects provided evidence that genetic factors contributed to variation in wing traits. Collectively, these results support evolutionary responses to long-distance flight in monarchs, with implications for the conservation of phenotypically distinct wild populations.
